High EMS Destroy ideally (my personal opinion obviously) is what I'd want them to canonize.
Control could work. As someone else stated (forget where, may even be in this thread I didn't go back to find it) who's to say that after rebuilding..ShepAI doesn't shut-down and/or destroy the reapers basically leaving the galaxy "rebuilt" but minus the reapers (essentially a "rainbows and butterflies" DESTROY ending)
Synthesis....meh. I despise it. And I'm not going to go into why. But it and "refuse" are the only two endings they should absolutely ignore. And "refuse" will have to be ignored if they keep it in the same galaxy...leaving just the abortion that is synthesis.
Even if they chose Synthesis (which while it may be interesting for a spin-off..doesn't really hold much substance for a continuation) I'd still prefer they "canonized" one of the endings and STAY in the Milky Way.
If this "leak" is true about moving to the Andromeda (or any other) Galaxy...aside from the trite of it being a cheap way out of their own ending garbage...it will make Mass Effect lose something. It'd be like moving Star Trek to another galaxy or Star Wars. ME started, and should stay, in the Milky Way. To do otherwise would absolutely take away the "human" element of it.
It's why you see in almost any sci-fi the main character(s) are humans and not some alien. Of course some will be perfectly happy with a Turian or whatever main character, but the majority will not "relate" to them as much and it will turn too many away...and moving ME out of the milky way will be similar...I really think they need to keep ME in our own galaxy.
suck it up, chose a "canon" ending that allows the series to go forward. I think they run the risk of losing less that way than some trite stunt this "leak" is proposing they're doing.