Two things that don't smell good.
First, "the change will occur through additional cinematic sequences and epilogue scenes", followed by Casey Hudson's "“We have re-prioritized our post-launch development efforts to provide the fans who want more closure with even more context and clarity to the ending of the game, in a way that will feel more personalized for each player", doesn't really sound like they're actually going to address any issues. It certainly doesn't make the "indoctrination theory" seem plausible at all. What it sounds like to me is that they're going to make a few voice acted cinematics, then code in a system that will check your saves for your choices and decide which ones to play. I could be wrong, of course, but it sounds like they won't be fixing the problem, but rather attempting to tell us why the current endings do make sense after all. And we'll still be stuck with the tri-color nonsensical ending, just with a bit more trimmings on the side.
Secondly, "coming out this summer" is actually a long time for something they supposedly "planned in advance". If they had planned it in advance they'd be ready by now. "Coming out this summer" means "let's try to do some damage control with the fans, can you guys make the loudest of protestors go away with some DLC whipped up in 2-3 months?"
I really hope I end up being proven wrong on this, but this announcement does not sound to me like anything that will actually wash the bitter taste those last 10 minutes leave.