Uh, no, you absolutely can upgrade graphical fidelity without changing engines. See Homeworld 2 Remastered for proof. (Homeworld 1 was remastered too, but it was moved over to the Homeworld 2 engine.) And UE3 is absolutely more up-to-date than the Homeworld 2 engine was.
An engine is just code. Graphics code can be updated.
I never said that you couldn't modify UE3 any further. But it isn't nearly as easy as you are implying, so why go through that trouble when you can use the latest generational version or another? What you and many other people here don't seem to be grasping is that for a remaster to be worth it, it has to be an improvement over the first. The ME trilogy made extensive and at times unnecessary use of LODs, particularly with regards to textures. Ambient Occlusion was switched off, so was anti-aliasing and a host of other relatively minor features. These graphical settings and constraints can be altered by modifying the ini files, and would only minimally increase visuals. This is something the user can do on their own, and would not warrant a remaster in the slightest. Now whether they choose to modify their version of UE3 - which would take more time and work than many here understand - or choose a newer engine such as UE4 or since EA is pushing it hard FB3, they will still have to update the environment and character assets, among a myriad of other things. That takes an incredible amount of time, especially optimizing assets for physically based rendering engines. ME1 > ME3 are all using UE3, but slightly different versions of it. They were able to implement new lighting models and shaders in UE3 ME3, but it was still built upon UE3 which to a degree is finite in what you can do and what is worth expanding. Skin shaders in ME3 for example were more expensive than new, optimized shaders in next gen engines which look better to boot. It's like trying to compare an old incandescent light to a new CFL, which can burn just as bright but for fewer consumed watts.
The sort of remaster you're describing is more of a remake. I don't think anyone's expecting ME1-3 rebuilt for Frostbite. It would be like creating a whole new game. They already have the high poly meshes and hi-res textures saved somewhere from when they were originally created (before being shrunk down to fit the technology of the time). The Unreal Engine can be pushed a lot further than it was for the Mass Effect games. Look at the weather effects from multi-player that didn't make it into single player or anything that the modding community has done without the benefit of having access to the best tools for the job. My heavily modded game already looks pretty slick and runs very smoothly without even being optimised to do so.
All of that is beside the point anyway. The fact is console players that have moved on to the newest generation of hardware no longer have the ability to play this game and neither will potential new customers unless they release a new XboxOne/PS4 version of the game. That in itself is a reason for a remaster even if it doesn't come with as many bells and whistles as you might have hoped.
A remaster is essentially a remake. Bioware uses Zbrush for their character work. For these games, they were retopologized - optimization of polygons and edgeflow - for what the current generation could handle. If they were to do a remaster of a game that didn't come out that long ago, logically it would make sense to do so with a next gen engine whether it be UE4 or FB3. Like I mentioned above, even if they tried to squeeze a little more power out of the UE3 engine they would still have to rework the characters, environments, textures, particles,and more. That doesn't change. So lets say Shepard's default armor is 15,000 polys currently in ME3. A lot of the detail is in the textures, and the textures are not optimized for PBR. They would have to reopen that zbrush sculpt, retopologize - which is quite a long and tedious process - the armor to take advantage of an increased polygon limit, recreate the UVs to account for the additional object detail, rebake the texture maps, and then optimize the masks and roughness maps for a PBR based engine. For every character and set piece.
I'm not entirely sure why you got the impression I'm hoping for any bells and whistles, there is no doubt in my mind that we will not be getting any remastered games - ME trilogy or KoTOR. It just isn't worth the amount of time that it requires, they're better off selling new titles than putting in the amount of work required for a remaster that won't sell as well. The problem you outlined above is only confined to those who play on console, and is one of the many detriments of doing so. PC users can still play games from decades ago, it's backwards compatible.
But this is the twitter thread, we've already gone a great length into this topic here even though it was based off of a tweet.
1. Nobody's ever confirmed a Mass Effect remaster.
2. How is that relevant to the Dragon Age twitter thread?
Because it was referenced in a tweet. Are you the only one who's allowed to elaborate on them now? I do recall you made quite a lengthy crusade in here regarding the exclusivity of the first DLC.