Well, the 'final verdict' isn't too obvious. The best source we have is an article in "The Badge" which is the TPS internal newsletter. It said that they are currently (mid-2008) in the process of rolling out new radios city-wide with 4 District being nearly (now totally) complete. It went on to say that the roll-out will be complete by 2012 and that the system will be capable of enhanced digital security. Note it says capable. That's where the guessing begins and the speculation goes out of hand.
The way I see it (in my opinion), one of two things will happen.
1) They keep things exactly the way they are right now, and simply change from analog to digital voice
2) They'll upgrade to a fully P25 system which means everyone will have to be digital (analog is impossible on a P25 system), and will be using 9600bps instead of the current 3600.
Of course, in either case, they COULD opt for encryption for some or all of their comms. No matter which option above they'd end up going with, we can still listen but if they encrypt, we're SOL, period.
Personally, I think they'll go for the P25 system as there's really no gained benefit of simply keeping the current system and using digital voice instead of analog. There's just no logistical gain and it isn't worth the effort.