I don't think Bioware will dare to get rid of any races from the trilogy. Too many people love them, and I can hardly imagine a Mass Effect game without krogans or quarians or geths. It's almost as impossible for me to imagine as a Mass Effect game without turians or salarians.
That teaser trailer had a Krogan in it (I'm 99% sure it's one anyway) and I agree, I can't see BW getting rid of any races: that would be mental seeing as they have created the best alien cultures known to Science Fiction.
I can see them taking a back seat to a few new races though if we travel outside of the Milky Way... god I hope it's a sequel (not running alongside the previous trilogy); I prefer not knowing what's ahead, etc.
I know that will mean choosing a canon ending, unless they go the DA Keep route...which would make sense, that way they could make up a reason for each ME3 ending to end up however the next game starts.
My guess is both. It will take place in another galaxy, but long after the Reaper War. This way, if it is about offshoots from our galaxy who left during the War settling in a new one, they'd have had time to build new civilizations on the planets they find. And they don't have to deal with ME3's endings. This also provides a new setting for the ME series going forward in which they essentially never need to deal with ME3's endings, which honestly is probably for the best.
I'm down with going to another galaxy, but not at the expense of totally ignoring the previous races etc ; a bit of both would be great though.
Say, a new threat emerges threatening the now rebuilt Galactic community, we chase after it into their Galaxy to be diplomatic and/or strike at it's core: discover new races with our Krogan/Salarian/Turian/Volus/Asari et al new team mates; make love to new colorful aliens... oh yes, that would be my kind of ME4!
