It would be nice to have one or more of the surviving classic Doctors in the special, but I don't think its a deal breaker. I've been a fan for close to 25 years and I'm willing to judge the special on what it is, not what I wanted it to be.
"Canon is only important to certain people because they have to cling to their knowledge of the minutiae. Open your mind! Be a Star Trek fan and open your mind and say, 'Where does Star Trek want to take me now'." - Leonard Nimoy