Generally there should not be any problem if you switch to 2,4 gHz radio.
They also work without BEC
The main difference to older radios is the method of transferring the data from Tx to Rx. In most cases you donīt find the classic ppm-impulse set in the transmission path (most 2,4gHz transfer the data "digitally") but the output of the reciever is generally the same.
BUT, there may be some differences:
The repetition rate of some 2,4gHz recievers is much faster (~10ms) instead of 20-25ms in the older times. This causes some rudder servo and also some very few ESC to do stupid things. In my experience this is a matter of trial and error, most ESC work but some donīt.
As mentioned above, some new Rx set the impulses for all channels at a time, so you need a much better current supply to the reciever.
I had a lot of different 2G4 radios in my hands, and never found a "wayward" neutral point, they all have 1,5ms in neutral.
Only a few old multiplex radios use 1,6ms as neutral point, but none of them is 2,4 gHz.
Iīm not so sure about the failsave while turning on, I never recognized something like this, but I would not except that this really exists. At startup 1ms to prevent plane esc from starting.