For some reason the general concensus is that the next class is gonna be some deriviative of the Amazon from D2. It makes sense that they would create a second bow class ... as right now Bows are quasi exclusive to Demon Hunters.
Story Line is gonna be either Imperius or going into hell itself to rescue leah.
And some leak basically said we are getting some runeword like system in the next expansion (my guess is we are finally getting the charm system they tried to implement during the last 2 releases).
I'm overly hyped before we even get an announcement :(
A level like descent to hell like in 1 would be amazing, nostalgia everywhere xS
I think blizzard should add a new act, but also add more content to the existing acts. Since everyone stays in adventure mode all the time.. and you only play through the game once... lengthening the game wouldn't be a bad idea. For example:
Add the other lords of sin. We really only have lust and gluttony so far.