I really cant think of a good reason why you WOULD NOT have Mcgann at least. He is a virtually unknown Doctor and it would be actually something new and fresh in the special yet have a tie to the past.
Sadly, the fact he's so unknown is probably why they wouldn't
include him. For kids and the general audience, there wouldn't be that immediate recognition that you'd have with some of the others Doctors. Even after you explained who he was, they'd just be like "oh, ok. Well that's nice I guess..."