Just a quick reply for while I read through the posts.
A few people have been questioning the mass relays on why they're not open & thought it was either the comics or a later game answered.
This was answered in ME1 where they stated that Mass Relays would not be activated until the other end was charted and mapped properly in response to the Rachni wars.
As for the galaxy, I to believe that looks like Andromeda but if you take into consideration what was posted as what the original ending of 3 was to be, this very well could be the Milkyway going through a tragic gravitational anomaly in the galactic core & is starting to collapse in upon itself warping the entirety of the galaxy.
You know, I actually thought of this too - perhaps it is the Milky Way utterly destroyed by dark energy - aka Drew's original plot. But then I thought - "no way they would just adopt that plot after retconning it with the organic-synthetic conflict. And besides, it doesn't avoid ME3: you'd have to address canonizing an ending still".
But, could be man, could be.
I think we can summarize the thoughts on what has been dubbed "Ark Theory" (or rather, hypothesis) as follows:
ASSUMPTIONS:
1) it assumes that Bioware deliberately showed us an image of a new galaxy map to generate hype/speculation as a clue to the setting of ME4. This galaxy map is not a "place holder", although it is likely a rough draft of the finished product.
2) The former assumption means that while any evidence at this point is circumstantial, it is significant with regards to the setting of the game as this image was deliberately shown.
3) The presumed reason why bioware would go this route is because, as they stated, they wish to ENTIRELY avoid the story and ending choices of ME3 and start fresh - at least for the time being.
OBSERVATIONS;
1) The image is NOT that of a barred spiral galaxy, therefore it is NOT the Milky Way.
2) It does not appear to be a star cluster based on the circular and relatively flat shape and vaguely spiral structure.
3) It most closely resembles images of Andromeda, lacking a distinct central bar and a logarithmic spiral shape to the arms. Comparisons between the infrared and ultraviolet images of Andromeda are easiest to see, although the combined image in visual light likewise adheres to this same structure, it is just difficult to see.
4) There is a branching, blue "energy-like" pattern throughout the image, most intense close to the center, which is not reminiscent of anything in real-life cosmology. It may either be the hologram "firing-up" or indicative that the image is not that of a galaxy, or that something else is going on (see below).
POSSIBILITIES:
1) The image is Andromeda.
2) The image is of an unknown galaxy that is similar in appearance to Andromeda.
3) The image is of the Milky Way, but of a Milky Way that is undergoing massive structural changes due to the buildup of dark energy to the point that it is unrecognizable.
4) The image is of an unknown celestial object, such as a worm hole.
More can be added as more people come up with ideas. (1) and (2) and (4) are consistent with Ark Theory or a story that takes place in a region of space that is completely cut off from the Milky Way.
Number (3) is inconsistent with this concept. It would be a story in the future of the Milky Way in which dark energy has obliterated the structure of the galaxy. I guess you could call it "Dark Energy Theory". Personally, I think the circumstantial evidence for that is significantly less, but it is interesting as it IS a plot that we know existed at some point.
So, since everything is circumstantial, I think those are all on equal footing at this point