I still like the idea of an epic "time travellers assemble" concept for Moffat's eventual send-off, though I'm becoming very confident now that that won't be in 2015. Hypthetically speaking, I now imagine the Series 10 finale to be his goodbye. As such I'd personally like to have River Song and Jack Harkness return in the same story, maybe bring back Clara as well (or a splinter of her would probably be more interesting) given she will probably and rightly be gone at the end of Series 9, the Paternoster's and maybe even daughter Jenny all in the same story - an epic two-part affront to the Weeping Angels set across multiple time zones and concerning an infamous moment in universal history.
For Series 9 though I'm happy leaving it at just Missy and Kate Stewart. In terms of threats I suspect the Daleks will be back on board, though perhaps only in a very small role if the Davros stories are true. I'd prefer new aliens beyond that, though wouldn't object to seeing the Sea Devils realised in NuWho for an episode.