Though I could see BF being leery of doing crossovers too quickly, wanting the cast to stand on their own ground and not have main Who characters bail them out too much.

Well, yes, but April in the wrong body is a bit beyond what the gang with their own means could fix.

Courtney Woods: I had been hoping we'd see her on the show, and yes, a return would be most welcome.

Re: school-themed menaces, well, there's the obvious Buffy precedent. And speaking of precedents, Quill having a dangerous son (presumably super fast growing due to his conception?) brings irresitably Connor (as in Angel's son Connor) to mind.

Shirtless in the woods: methinks Patrick Ness has read Maurice. :)