That's been a rumour since The Lodger last year due to some logo similarity in the design of the TARDIS in that story (which was also in this one, of course).
It seems a bit random though- Moffat has gone to the trouble of creating a neat new enemy, and I am unsure if any connection to a classic foe like that is needed. Still, we'll see.
Press reaction has been a bit mixed for the same reason I noted above- pacing-wise, this was a heck of a jumble. But I think it's mostly won high praise from the nerds.
Here's a prequel clip of the next episode