Well of course the planes would be extremely expensive and locked behind very hard to get licenses. I'm not saying it should be reasonable, and definitely not easy, all I'm saying is I think it should be possible. It could limit the RP for LEOs true, but it would massively expand the RP for alot of other factions, and maybe even add a whole new faction - the military which would intercept planes or helicopters.
So I guess the question is is somewhat limiting LEO RP worth it to expand the RP for several other factions. Besides it might not limit it that much, with helis the PD can give chase directly, and with planes it'd probably be NRP to land not at an airstrip, so the police could be waiting for you when you land.