"Actually I think it would be an ingenious way to sell out nearly every show for a three month run, and each purchase would likely be full price - no one would wait for TKTS or reduced tickets and people would likely hit up their favorite, anyone they missed, and John."
I think you're underestimating how much work it is to get up to speed and do this show. For that short period of time, it wouldn't be worth it to the actors. Plus, it would be Neil's show to close out, really, since he is the one responsible for getting this production mounted, he won the Tony for it, etc.
And I say that as someone who didn't like him in the role and worships JCM. 