They'd have to rewrite major portions of the story starting in ME2 and retcon reapers back to their original intention. There's simply nothing Shepard can do that could ever compare to dealing with the reapers, they're a galaxy-wide extinction event.
I wonder how much they kick themselves for writing themselves into a corner like that. Easiest way out would probably be an alternate universe.
I thought remasters implied minimal changes to the original content.
A remake of Mass Effect would be a great idea to resuscitate some of the original value of the intellectual property, which is why I am absolutely certain beyond all doubt that EA/Bioware will never, ever even considering doing it.
As it is now, they are just going to remind people in vivid detail why they are pissed off at EA/Bioware.
"Rotating crops" is utterly alien to EA's "slash and burn" strategy of buying up studios, forcing them to do dumb things, and then shuttering the ones that don't get the results they want.