Question, why won't the LTE systems be compatible? As far as I knew, once the carriers switched over to VoLTE, and sold off/scrapped the GSM and CDMA networks, any phone would work on any network... Is the reason you are saying that frequency based? Because manufacturers already accomodate that with the Quad and Pentaband phones...
Block C regulations require Verizon to allow any compatible LTE phone on their network, and allow any phone Verizon introduces on their network to be freely moved to another, compatible network.