Here is the little update of the OP.
I tried to collect all the information on the Keep there is for now. I hope this helps people to answer their questions.
What is the Dragon Age Keep?
Within the Dragon Age Keep, you’ll be able to customize a Dragon Age historical world state to your exact specifications drawn from Dragon Age: Origins and Dragon Age II story decisions. These include hero attributes, companion details, quest results, and more. Customize as much or as little as you wish. Then you'll be able to import your saved world state into Dragon Age Inquisition at the start of a new game. For new players, the Keep will serve as a great way to understand the people, places, and events that shaped the world leading up to DAI.
Will the Keep be available in other languages than english?
The Keep will be available in every language the game itself will be, too. (english, german, frensh, portuguese brazilian, spanish, italian, japanese, polish and russian)
What choices will be reflected?
We don't know much about that yet, but it will definetly be a lot of choices. Cameron Lee said, there will be 300+ choices in the Keep.
It will contain all choices from Dragon Age: Origins, Dragon Age: Awaikening, Dragon Age 2 and all DLCs, no matter if you have bought and/or played them.
If you leave some choices uncecked, they will be filled with a default decision. That goes for DLCs aswell, everthing has happend, one way or another.
Will there be traditional Save-Game-Import?
No!
Why not?
There were many bug issues from DA:O to DA2. This is the easiest way to do it. Furthermore the Keep gives people, who are switching platforms or people who lost their saves the opportunity to re-build their world states. And it also give people new to the franchise the opportunity to create a world state and learn about the lore of Thedas.
What's the Default-World-State?
A female Dalish Elf Warden, who made the Ultimate Sacrifice, Alistair is King of Fereldan. And a Mage Hawke, who sided with the Mages.
Will I be able to import my world state to the Keep and customice it?
You can't import your save game, but if you had your previouse heroes uploaded to the BSN, the Keep will pull them over. And then you can alter it, if you want to.
Will there be a CC to re-create my Warden and/or Hawke?
No! (Not in the Keep. Should your Heroes from previous Games show up, you will have the opportunity to change their looks, but that will happen in-game!)
How can I access the Keep?
The Keep is a website. You should be able to access the Keep with any browser, even on a cell phone or tablet. You just have to log into your Origin Account and then you can save your world states.
How many World States can I store in the Keep?
As of now you can store up to 5 World States. One of them you export. That's the one DA:I will load, if you chose to import.
How can I import my world state from the Keep into the game?
When you start a new game in Dragon Age: Inquisition, you can log into your Origin Account and choose to import your active World State.
Is there an offline solution?
No. As of now, there is no option to downloade any file and import it via USB. You have to be online to import your world state, then you can go offline.
This is not possible, because Bioware cannot creat Xbox or PlayStation save files. Microsoft and Sony won't allow that!
When will the Keep launch?
No release date yet. Approximately a month before DA:I.
Also see the Blog Post.
Here is a little FAQ by Fernando Melo and here is another FAQ in the 'News and Announcements' section.
Fernando Melo, on 25 Jun 2014 - 11:53 PM, said:
All done with this wave of invites - hopefully that got to some of you. Better luck on next one to the rest.
Also, just to help with some common questions/conversations, in no particular order:
- DA Keep will launch before DAI. Sometimes we will figuratively say 'month' or 'months' but at the end of the day, there is no exact date yet. We have our target obviously which is in that timeframe, but the real date will be determined as we get closer to that target. It will depend on many things including how our beta testing is going, and how/when in the DAI communications plan is the right time to talk about it, and ultimately how soon before DAI to open the doors to all. Believe me, once we have a date locked we will definitely make that known.
- DA Keep is alive and well. We've been letting in beta users since late Dec. Purposefully, the numbers were very small to begin with. That helped us ensure even bare basics like beta login and feedback mechanisms (critical for a successful beta) were all in place and working as intended. The lower numbers also meant it was easier to collect more qualitative/verbose feedback on features, and react early enough to that. As we get closer to launch, we can now let in more and more users with each wave. Ultimately, as we get ready to open doors to all, we'll shift more into load testing where we will be letting in the largest waves of users.
- Why do I still not have an invite? I wish it was possible to just let everyone in, as it is awesome to see so many of you genuinely interested in participating. But a few logistical reasons: 1) We don't select by date applied - so applying on day 1 does not guarantee you're first in. 2) Depending on what they are looking to test on any given wave, the team will select applicants that match that criteria (that could everything from level of experience with previous games, to what you wrote in your app). 3) From that group, the team then randomly picks out a rough target number of users for the wave. Again, depends on what they want to test, and accounts for enough % of folks that may not respond in time. 4) Odds. Even as we're adding more beta users and increasing the size of each wave, we continue to get more beta applications - so I would guesstimate that we are probably around 3-5% ratio of beta users to applicants. This will continue to get better over time as we add more and more users, but that is a big factor in why so many have not yet received an invite - reality is that the majority have not, sadly. Not yet anyway. 
- DA Keep does not use any files whatsoever. There's no import (although we are still continuing to look at this, the priority remains with getting the rest in place and solid), and there is no file based export. That means you don't copy any files around, or use a USB or anything like that. You login to DAI, opt to sync from Keep and DAI grabs the data it needs, and you're done (you can actually logoff/disconnect at that point if you want, and can play rest of DAI with no further Keep logins needed until you want to start another game and import a new world in).
- "Lots"™ of choices. Mark mentioned in an interview that there are over 300 so far, which is accurate, and we continue to add more at the request of the beta users so far. Obviously (I think), not everything will be reflected in DAI. The purpose of Keep is to capture your world as faithfully as we can for future use. Before we launch we'll reveal more info on Keep, and as part of that I'd like to get you a better idea of what you can expect.
(semi-legaleeze) Make a note of the time and date of this post - this info is correct as of 'right now'. Plans do change though, and we may need to revise those statements over time, but for now that is where we are at. (/semi-legaleeze) 
And here some Videos with information
Video Interview by Gamermd83 with Fernando Melo
Keep 101 by Lady Insanity
DAK Info and Details
A Keeper Talks with Gamermd83
First official reveal of Dragon Age Keep! (August 29th 2014)
youtu.be/3rNDZ0Ih3v0
And here is my summary of the important informations:
- The Keep will synchronise with the BSN, so everthing you had uploaded there (unlocked items, Achievements and your Wardens and Hawkes) will be pulled over to the Keep. There you can choose one of your heroes, if you wish to and start with their uploaded decisions. You can still alter them, if you wish to.
- If you start the Keep again and you have unlockled new Achievements, they will be updated.
(Note: I don't know if this will happen from the games directly or through BSN. Personally I hope, it's the first, since many (me included) have issues with that. Our progress is not uploaded)
- There are also pre-made Heroes you can choose from, so you don't have to start from scratch.
- You can view your story in a wonderful video narrated by Brian Bloom (Varric). You can edit your choices during the sequence and it will be reflected.
- Should you make decisions that are incompatible the "Auto-solver" will warn you and force you to correct that. (i.e. if you select 'Stens Sword was recovered' and then say 'Sten was not recruited' you have to change one of them.
- The Keep is a work in progress, so for now there are 200 choices actually imported into DAI, but that can still increase.