I've always loved Sera as a writer so i hope she will write some episodes even in season 8. As a showrunner she was far from perfect but i can't totally blame her because she didn't know how to be a showrunner in the first place and Kripke didn't leaver her too much to work with since Swan Song is basically a series finale.
I LOVE Carver, i've pratically loved every episode he has written and unlike Gamble he has been a showrunner in another show so he knows how to make things work. And since Being Human US has already been renewed for another season he could have stayed in that show if he didn't have some good ideas for SPN. So i'm totally optimistic for season 8 and curious to see where Carver will take us.