But it doesn't have to have hit all of charted space. That's the thing, you can retcon whatever you'd like. For Example, in ME2 you can destroy the collector base or preserve it. But in ME3, the novels set post Me2, and the omega comics, it's retconned that no matter what choice you made, enough of it is in tact for cerberus to utilize its technology for their weapons programs.
You could do the same here. In fact you don't need to even address the endings. Would anyone really be angry if they retconed it but kept it so that you could at least believe humans could exist in this other galaxy.
We don't know this, and its not stated that this is the case. This assumption was made for places like the Rachni's home system, and the Sol System. Because nobody was allowed to explore them.
Great! Where are we gonna go when they **** up Andromeda then? The Triangulum Galaxy?
It's such a dumb idea to set this story in Andromeda. Because what it says is that no matter how much potential something has, the teams main solution hasn't changed since mass effect 1. If there's a problem, cut it completely, and never fix the problem.
People don't like how the skill system was implemented in Me1? Cut it completely for Me2. People don't like how bad the Mako handles? Cut it completely for Me2. People don't like how weak the Hammerhead is in Me2? Cut all vehicles from Me3. People don't like how lacked the skills are in Me2? Cut it completely in Me3, just bring the old one back and nobody will notice.
Only you can't run this kind of change back. You can't run back going to a completely new galaxy. You can't just say "Me5's gonna take place in the milky way again". There's already so much space magic just to get us to Andromeda. It's ****** far away, and there were much more inventive choices. Hell, we could have just gone through all the Local Group galaxies, like Sagittarius Dwarf, or Ursa Major, Or Draco Dwarf.
Hell, look at this.

Look at how many dwarf galaxies circle the Milky way! If you're going to leave the Milky Way, you could have just had us going to all of these! Imagine a galaxy map where you travel around the milky way, and how huge the game could have been. Hell, you could literally have an expansion into another one of these satillite galaxies.
But Andromeda, despite having a cool name, doesn't have this sort of clustering, or at least not nearly as much. Added onto that, the fact that none of the speices we'll encounter will be native to Andromeda except for the bad guys, and you already can tell this game might as well have stayed in the Milky way.
Tell me something, how many new aliens have we been shown since the announce? Has the dev team said anything about us encountering new aliens?
No. How many fans here are clamoring for new alien races? Basically none. They make up about as much of this fanbase as explored space does in the Milky Way, 5% or Less.
People want the Asari in Andromeda, They want the Quarians In Andromeda, They want the Drell in Andromeda. We already have our first alien in the teaser, and it was a goddamn Krogan.
What exaclty am I seeing that's so special as to warrent this being "A New Galaxy?" Whats so new about this Galaxy that makes it different from the Milky Way? Besides a **** ton of questions and asspull magic that's never gonna get addressed? And that's talking about us getting to Andromeda alive and still recognizably human. That's not even addressing the endings, which still need to be addressed to say why there's an Arc going to the Andromeda anyway.
Where's the new content? Where's the new galaxy part of this Galaxy? Because what I'm seeing is the Milky Way, with its name crossed out, and the word "Andromeda" written in sharpie. If they're going to set this in a different galaxy, make it goddamn different. No humans. No familiar species. All new creatures. Want them to resemble humans? Fine. Make them blue humans for all I care. But don't make them straight human. And don't bring up the goddamn N7, which is something that only matters for Earth, a place we will never see in Andromeda.
If you set your game in the United States this whole time, and then said we're going to Japan. Don;t have Arizona Mesa's and Cowboys with lassos running around the game, and still try to claim its japan. Don't lie to my face and call this different, when its not different in any single way.
I think you lost your marbles bro.