I think the way forward is the box that plugs into the remote cord connection and communicates using the 900mhz band with the remote. That would seem like a development that is quite possible. If the existing DCS Remote works well with the port on the "new" TIU, I can't see why this isn't the way to keep using the existing remotes.
Seems very doable. Part of me wonders if the ability to plug in a 900 MHz transceiver somewhere in the signal path might already exist. I thought I read somewhere there is little difference to the signal that the remote sends to that of whats on the center rail, just modulated differently.