A change of setting is just a change of setting. A hard reboot is like Spider-Man 3 -> Amazing Spider-Man.
This is exactly why i despise reboots of franchises nowadays. Amazing Spiderman is disgusting piece of degenerate sh*t compared to the "originals" which weren't even all that good(still tolerable). Various other reboots(Terminator TV series, last Star Trek movies and the series, even the last Star Wars movie) are getting just worse rather than better compared to originals because there are hardly new impulses or stories, it's just repeat of the same setting, same characters, same time frame in a supposedly new yet actually worse interpretation while the things that were originally making the franchises interesting are slowly marginalized away.
Rebooting ME series would mean to discard absolutely everything about Shepard, about the story, the characters, everything players accomplished. The way they tried to kill off ME franchise with ME:3 is already - mildly said - irritating, making a reboot now would be basically spitting in player's collective face.
Just think about what Bioware story writers or whoever was overseeing/directing the main plot have tried to do:
They "took away" Shepard from us by introducing lots of auto dialogue and loading the protagonist up with some emotional crap we did not care about much - that annoying kid Shepard suddenly worried about.
Then they did everything in their power to kill off Shepard, to end the character so they would not have to continue Shepard's story, because, according to tweets and interviews, they were tired of Shepard and somewhat tired of ME. Okay this is understandable, after 3 games some creative people might really want to try something new.
But no, this wasn't enough, they just went and *literally* nuked their entire franchise to hell. The entire franchise in a single stroke, by killing off the entire Milky Way galaxy. Here, have some galactic Dark Age, no more ME for you. Also F**k you, thanks for playing, plis gib more monies - right there in the middle of your screen, while you sit there, dumbfounded by what the heck just happened.
They basically took what all of us liked so much and smashed it to bits right before our eyes, while cackling something about "artistic integrity".
And now you serously think a reboot would be a good idea? More like a giant middle finger to the most of the playerbase.
In my opinion, ME1-3 should be aknowledged in ME:A, Shepard needs to be an important historical figure(certainly one of a kind hero of humanity), Reapers a topic among scientists and historians(ie discussions about whether or not they were or could come to Andromeda). Not only that, but we should be given a chance to come back to Milky Way in another installment of ME:A series, to explore what happened to the galaxy we left behind. I outlined a possible way to handle the ME3 endings in such a case or we just go with IT theory where Reapers won and we suddenly face leftovers of Reaper force eradicating the last remnants of the dying galactic civilization.
Going back to Milky Way, now as strangers and outsiders, would make a lot of sense from a story telling and marketing point of view anyway, in my opinion.