Just to chime in quickly here about the packet side:
I guess a smaller vision would be to see a software TNC like direwolf that can natively support more than one over the air baud rate.
This is already possible today with Direwolf using .asoundrc tricks. The problem is, all other stations on frequency won't necessarily recognize this faster mode as a valid signal and thus possibly double on that signal. As such, it's better to use other frequencies for newer modes. All that said, I do understand your desire to support a "transition" approach.
--David KI6ZHD