If you replace your TMCC Powermasters with the new Legacy Powermasters, then if you upgrade to a Legacy (CAB-2) or CAB-1L system in the future, you can just swap the base unit (Assuming that you will no longer be using the old CAB-1 system.) and use them without the need for a Bridge unit. Even if you use the old CAB-1 system alongside the Legacy system, you will not need a bridge.
The new Legacy Powermaster communicates to the base via the track signal, and not via a radio connection. So no frequency converting bridge is needed. You can connect them to a TMCC system, the full Legacy system, or the CAB-1L system.
i have several of the Legacy Powermaster units, and they perform beautifully in conventional mode.