A Bleeding Cool report about Matt Smith phoning Clara to tell her about regeneration has been going all over the Internet. Not that that'd require a full-blown cameo as the Daily Mail suggests, but it is entirely possible we'll be hearing from the Eleventh Doctor one last time in the next season. It'd fit with Moffat's fondness for temporal shenanigans, at any rate.
Meantime, Doctor Who TV has a snippet from a convention last week: "Don’t ask. I’m really possessive over Alex [Kingston]. I said this to
Steven. I was like, ‘Listen, just don’t! Just not Alex. Anyone
else, but don’t give [Capaldi] River.’ But Peter is the Doctor now so
hey, what can I do?”
So maybe that's why Moffat's been a bit standoffish about doing more River stories. Or they happen to be in agreement that that story's come to a natural end. Alex Kingston herself has been fairly cagey as of late, but then she's got a lot going on right now: an upcoming Radio 3 performance of "Antony and Cleopatra" against Kenneth Branagh (you can guess who's playing who), working with Noel Clarke in a new ITV drama, "Chasing Shadows", there's new episodes of "Arrow" with her in...
Zap2It dug up a deleted scene of Smith from "In Bruges" (he's playing a to-be crime boss).