It was hilarious using the scene that was done for his vacancy in the 25th now that he can't be here for this 50th piece of fun.
"The Five Doctors" was the 20th anniversary. The 25th anniversary story was technically "Silver Nemesis," though nobody likes that one much, and the slightly earlier "Remembrance of the Daleks" works much better as a 25th-anniversary story.
And just to be even more nitpicky, the scene was actually filmed for "Shada," and was cut into "The Five Doctors" when Baker declined to participate.
But yeah, this was a lot of fun all around, and I loved all the in-jokes. Awesome that they even got Peter Jackson and Sir Ian McKellen to appear! And I loved the riff on the "Androzani" regeneration scene with all the old companions swirling around -- I'd have to watch that scene over and over to catch all the cameos. (Or read the credits. I caught Lisa Bowerman's name!)
So I suppose that since this had Moffat and RTD's involvement, was shot in conjunction with TDotD, and had the BBC Cymru logo and all, that makes this an official anniversary production even though it didn't air on TV. And that means that all the surviving Doctors, except Eccleston, participated in anniversary productions in one way or another. Which is great. (Although it's possible some of them may have had voiceovers in the climax of TDotD. I couldn't tell, since all the voices were overlapping.)
It occurred to me this morning that Colin Baker could've conceivably had a cameo in TDotD as an aged Commander Maxil. He could've been the general in charge of the war council! If only...
Anyway, I am really impressed by Peter Davison as an actor these days. I love his performances. I don't think he stood out quite so much when he was the Doctor, but he's gained a lot of gravitas and power now.