is there any indication of NYSP or some other state agencies joining the system?
Nope. NYSP is probably going to stay on their VHF, it has gotten progressively better over the last few months. I know some other NYSP Troops statewide are ditching VHF and hopping on local counties' infrastructure, but with Troop K at least this doesn't seem to be the case. I heard they might be testing some new repeaters to improve coverage. Nothing as far as other state agencies like NYS DOT etc.
But this thread is discussing the county UHF Paging Frequencies, not the A66 system.