In Florida, we have a toll transponder system too. Recently waves of notices have been going out that the older style transponders are being deprecated for newer ones. I always thought that was kind of silly because the new style transponders are currently compatible with the existing system just like old ones are, so it's not really a "protocol" type change (I'm a software guy, not an EE, so there is likely some RFID stuff I don't know about).
The biggest change? The older transponders would beep when scanned, the newer ones no longer have that functionality. Sounds like perpetual tracking is coming to my state.