Talking to Doctor Who Online, Gaiman said:
He then went on to express his excitement at writing for Peter Capaldi's Twelfth Doctor:"They would like to have me, I would like to do more. The only problem I'm having right now is the time that I probably would have spent writing a Doctor Who script this year suddenly was eaten by going on tour. I would love to write an episode for Season 8; it may well be that I’m over in Season 9, but I promise I haven’t gone away."
"The idea of writing for Peter Capaldi’s Doctor is one that I find so thrilling and exciting. I’ve been a fan of his since Neverwhere."So while Gaiman might not be back for Series 8, we'll certainly see him penning an episode at some point in the future, possibly for Series 0.
[Source: Den of Geek]