Apparently the only reason we didn’t get to see the TARDIS swimming pool room in The Doctor’s Wife is because Karen Gillan doesn’t know how to swim!
"Making television - and especially making Doctor Who, where you have to imagine a new world, in my case a new universe, with every episode - is always a negotiation between dream and reality. (That was the same email in which I learned that we weren’t going to have the scene in the Tardis Swimming Pool because Karen Gillan couldn’t swim.)"
Source: Neil Gaiman’s Journal: A Fairly Humongous Doctor Who Q&A Mostly
(Scroll down to the question about “Why an Ood”)