Can i bind any rx to my ko propo ex1 or is there limits on what rx can be binded to tx'

There may be a couple exceptions but for the most part, all receivers are proprietary to the manufacturers of the transmitter.

Thats a shame, i was hoping to try the spectrum with telemetry rx's so i s'pose id have to buy the whole unit in that case.

There are even some incompatibilities within brands as the companies have developed their technologies. The only case I'm aware of where a Spektrum receiver works with a KO transmitter would be by using a Spektrum module in the KO.