Did you read what I said only the things that would be canon in the trilogy are Udina being counicler and the ending most choices in the trilogy only affect a few individuals not the galaxy. I wouldn't be surprised if something like the DA: keep was made to address rachni, geth and genophage even though they may not be relevant to the next game.
Ignoring the ending or trying to write around them isn't a good idea either since its going to harm them in the long run as trying to avoid them isn't going to make them go away. If you you look on BSN people are willing to have a canon ending if it means they get a better game as a result its not ideal but its a fair compromise and the endings can easily be address briefly it doesn't have into much detail as to what happened.
First, I honestly have no clue why you keep bringing up the Udina thing. I only ever mentioned it as a choice that as ignored and made a lot of people angry (A great example of why what you suggest is a bad idea). It's not like it would even matter if it was canonized, Udina and Anderson are both dead. Creating something like the keep doesn't address the endings or the Geth and Genophage choices, it just lets you define those choices. My point is that in order to adequately address those choices they would have to create several very different galactic communities, even if the ending is canon. If you plan to have characters interacting with the galactic community at all,mor if the history Shepard helped craft is to be more than a meaningless backdrop, that must come into play.
Trying to avoid them isn't going to make them go away? That's you're argument? Really? Okay, what pray tell will addressing them accomplish? Nothing, except to mire the next game in damage to control for the trilogy instead of ever getting a chance to become its own story. There's no way to satisfy everyone, as you yourself admit, so why this half measure of setting a canon, ignoring people's choices, and homogenizing away Shepard's historic accomplishments to meaninglessness. Do you really imagine this approach will somehow make everyone all happy with the endings and give everyone the satisfying closure you think the Extended Cut lacked? (It didn't, by the way)
Some people are satisfied with setting a canon, I don't see any reason to think they're more numerous than those who are not. In fact I think you'll find just as many like me that are vehemently opposed if not more. And honestly I think most of those that support a canon picked Destroy and are comfortable with it because they know they'll likely see they're story played out. I wonder how many would still support it if Synthesis or Control were picked as canon.
At some point you just need to accept that this is not "Mass Effect: What Happened To the Galaxy After the Trilogy" but "Mass Effect: A New Story". Shepard's story, and everything it concerned, was wrapped up in the EC epilogue, and we don't need any more details than were given. Just because you want the remaining life story of every named character doesn't mean it's needed or even desirable.