I mean nothing is stopping them from just setting a completely separate story during the events of ME1, 2, and 3 and tell interesting plotlines in an established universe and time-frame. The galaxy is fucking huge and a lot of planets have potential beyond being backdrops for shoot-outs.
But since EA and Bioware are completely on fumes and exhaust with their string of failures they HAVE to bring back Shepard and all the old faces. They cannot afford not to.

>>723530798
>if she's not satisfied your spine gets pierced and you have to watch as she eats you alive in a paralyzed state

>>712627969
>she doesn't know
stay blissfully ignorant, sister