I can only see Asura being the final boss in this if there will ever be an ending.
Maybe he will make the odd appearence here and there but I don't expect it to be long.
Soul's soul breaking is something I'm also expecting. I really hate that goblin thing inside his soul and I wish that he could have kicked him out already
I have to say that it is surprising to see that sid still plays quite an important role in this (and then you have to think about how he died >.>).
And if anything, I wish for the old Stein to be back ;__;