That's not "left-field" at all. Having the radio operate on 2.4 GHz does make it easier to put the transponder in the same case as the receiver. The transponder operates at 5 MHz, so it wouldn't cause interference problems due to the great disparity in frequencies.

I think that before a manufacturer would commit to doing this, we would need to have an accepted standard for transponder and decoder operation so that the radio manufacturer doesn't design something that can be easily obsoleted. (An example would be MIDI for electronic musical instruments. The manufacturers all got together many years ago and worked out a system, and the technology is free to anyone who wants to use it.)

We had a de facto standard for many years, created by AMB. Then MRT started making transponders. Now AMB wants to update their system so that only AMB transponders work. That's entirely within their rights, but it basically screws the racer.

What we need is another, competitive decoder that accepts all the existing transponders. I know of one manufacturer who claims to have a system ready for testing, and I'm currently playing with such a design.

If the technology for both transponders and decoders were made open-source, then we would have our standard. It's very tempting to do that.