I'm not optimistic. Remember all the press releases have pretty much been saying that the ending won't be overhauled or changed in a significant way. The only thing it sounds like they are doing is clarifying events.
Truthfully, there are SO many potential plot holes that they should have expected the fans to be upset. Did no one read the story? Was there not a soul who went "this may just annoy and anger a lot of the fans" or simply say "In the context of the situation we have created this makes no sense?" Or was this all fabricated in the beginning to create publicity...if so...I'm pretty sure the "all publicity is good publicity" motto does not apply here.
I am expecting extra cutscenes and dialogue that explains how everyone got back to the Normandy, what happened, clarification on who is where, and not much else. The fact that they have not stated that they are not opening new avenues for players is an outright declaration that they do not intend to actually consider their previous work factoring into the ending in the meaningful way the fans would like.
I admire that they stand by their work, and respect them for it on an ideological level. However,the last 15 minutes of the game simply did not provide closure or even reason for its happening. I loved the game, Priority: Earth was exactly what it should have been(an all out overly desperate run against an unending horde...because that is exactly what you are fighting against). But the ending did not provide satisfaction, and I am not alone in saying that whatever they were going for was not achieved. If they go back and clarify WHY things ended that way(because there is only 1 way) in a way that satisfies the fans I will be shocked and surprised, but the fact that they even had to is...problematic.