Maybe, but the fact that CE did meet with SM, SM had to show him a script or an outline of the story. So a story with a third doctor did exist (Let's face it, we always new #10 would be in the 50th no matter what). Since CE again has disappointed Dr Who fans (notice I said Dr Who fans, not CE fans), the story with 9 included may be able to be changed with minimal effort to include 8. UNLESS the story heavily involved all three of the doctors knowing Rose and Rose knowing 9 & 10.
I like the idea of McGann but to have 10 11 and ... 8 just seems unlikely. Maybe if they had the other classic actors involved but otherwise I think a lot of viewers might be asking "Doctor Who?".