The worst to convince to fight the reapers will be the Batarians... for obvious reasons. Perhaps they will be the reapers' dirty hands this time, since the protheans and the geth are "defeated" in previous games...
I suppose it's possible, but the Batarians aren't stupid, they just hate humanity (and Shepard even moreso, post Arrival.) I'm sure there will be some kinda reckoning with them, but out and out submitting to the Reapers? That would kind of a cop-out, and more than a little idiotic. IMO, anyway.
Yes I agree. And since the reapers arrived, one could say that their ability to mindrape everyone just exponentially increased. So we could have not one slave race, but several, perhaps all of them were partially mindraped and turned into slaves. So you will fight humans, salarians, etc.,etc.
Some basic guesses:
Miranda will be torn between her faith upon Cerberus and Shepard.
Kaidan / Ashley is still torn between Alliance and Shepard.
There will be blood between those three
Thane will die in the first third of the game. And it will be sad. Perhaps Shepard arrives too late (optional?) and only gets to see the funeral. His son will be there, at peace with his father.
Tali and Legion get their act together at some point in the game. Between the second and third thirds of the game. Both their fleets will be essential.
T'Soni will be more efficient than the whole Council at gathering intel resources to the war.
Illusive Man will go too far, but he won't be Saren-like. I hope. I pray
Rachni queen will be of some (minor) help, if your shepard didn't kill her.
The geth will be more powerful if you chose to brainwash them.
Mordin will have a hard choice, to release the cure for the genophage or not. This depends upon the nature of the war. If the war is to be fought for decades, then this decision is important.
Someone of value will die before the end. I'm betting on Garrus. Very emotional, Shepard gets furious, won't let it be in vain, bla bla bla.