Please no...
If you want to change a franchise, then change the things that DIDN'T work rather than add unnecessary additions. The Bioware storytelling is unmatched, and it doesn't need shoddy multiplayer murkying that up.
Instead, have ME3 have some sidequest mechanics that are just as entertaining as the main storyline. The crappy vehicle sections of the first were the worst part of the game, as were the exceedingly boring planet probing necessities of the second. For ME3 I'd like to see something awesome in the place of these rather than a raging emokid looking for a corpse to teabag.
Obviously with such a lack of information regarding where Bioware is planning on going with this, these concerns could very well be moot. I remain skeptical, however. I hope that I'm proven wrong.