I mean, I'd love for Paul Cornell, Robert Shearman, Marc Platt (he wrote Spare Parts; I'm around half an hour into that) and maybe Matt Jones to do more episodes. It'd be good for new, untested writers to do some episodes. I think the days of Gareth Roberts, Toby Whithouse, etc are over. Mark Gatiss can write such good things (his Sherlock episode was excellent), but he can **** up royally too.
Series 6 is bringing back the decent Tom McRae. It's bringing back Mark Gatiss. It's bringing back Matthew Graham (admittedly a good writer, but "Fear Her" was lame). And it's bringing back Toby Whithouse. I think it needs new writers.
They might bring back Robert Shearman. That guy is excellent. His book Tiny Deaths is highly recommended. Him, I don't mind.