Regarding the 50th.
Something like this you dont screw up. You have Baker, Davidson, Other Baker, McCoy, McGann nearing the end of their lives, and to piss this away for any reason just defeats the whole point of celibrating the 50th.
Say what? Since when is 53 (Paul McGann) and 61 (Davison) considered to be "nearing the end of their life"? The Bakers and McCoy at 69 and older, yes, definitely a legitimate concern that the opportunity may not arise again.
Not to say McGann or Davison are immune from dying/becoming incapacitated before a future opportunity arises, and I definitely want as many opportunities to see them all while they are alive as possible, but, to call call 53 and 61 "Nearing the end of their lives" is WAY over the top (Unless you know of some specific health threat they have, which I'm unaware of). Yes, I'm aware of Mary Tamm, Elisabeth Sladen and Caroline John the last few years, but, those are exceptions
It may or may not be near the ends of their lives. You can never be sure. But, consider the very low frequency of multi-Doctor episodes and it may well be true that the next one (if there is one) airs after some deaths. Also, even if they're alive, they may be retired from acting and too old to remember their lines/get around even if they wanted to.
Life is uncertain, they should be included now. Of particular concern is William Russell! They messed up with the Brig, let's not have history repeat itself!