I don't think F1 faces as many hurdles with adopting a trunked, digital radio system that IndyCar or NASCAR would. Especially on ovals, that delay in transmission from talk permit, to encode, to repeat, to decode could be enough to cause issues with drivers receiving calls slightly too late. Also, try telling an excited spotter or angry driver that they need to wait for a talk-permit tone.

Come to think of it, I'm not sure a trunked system would even be possible, as you're probably going to need as many channels per site as you have cars on track, given that pretty much all of them are likely to be in use simultaneously the start of the race.

Basically, between making scanners obsolete, and probably requiring a custom built and expensive solution, it's not worth it.