User blog comment:TheUnseelieCourt/Next Mass Effect To Be Developed By Bioware Montreal/@comment-2250460-20121112203419/@comment-213828-20121112214325

This isn't something you can just make cohesive with a few lines of dialogue like "Anderson resigned from the Council" or "the Reapers constructed their own Rachni queen" or "Cerberus salvaged tech from the remains of the Collector Base".

For something like a merged sequel that fits in with all the possible endings to ME3, "the organics decided to build a second Crucible and merge all synthetic and organic life for God only knows what reason" or "one day, the Reapers got bored with our galaxy and left forever". And that doesn't even take into account the Refusal ending. That would have to be decanonized and un-importable - like the "Shepard dies at the end of ME2" scenario.