I’ve been trying to figure out what I want to do for my mobile installation as well, to permanently replace my mag mount and CCR HT current setup, and I’m trying to figure out if I can/should “cry once” by going this kind of route versus my other leading contender the ham-specific TM-710GA. By what mechanism do the multiple RF decks play nicely through a single antenna? Or do they require multiple antennas, one per deck (per band, basically)? Can you add options/upgrades later like DMR, or must those be selected at time of purchase or not at all?
A diplexer will allow you to combine RF decks on different bands into one antenna.
If I was doing it, I'd go with separate antennas for each band. Diplexers have a small amount of loss, plus the selection of dual band antennas is kind of small. With separate antennas you can set them up the way you want.
DMR, P25, etc. are licensed options, so they can be purchased later on down the road if you decide.
Unless you specifically have a need (and license) to use the LMR channels, it's a very expensive way to do a dual band radio. For some users, the lack of a VFO is a deal breaker.
For a dual RF deck NX-5000 setup, your looking at close $2000 or more. The 710 is about 1/4 that price, plus you have APRS.