The Home Patrol family, HP-1 and x36HP, are software defined. Digital modulation, such DMR, are just software. It should be able to be updated with new waveforms as they are developed. SDR have that ability.
Seems to me that even if the possibility is there, it won't happen. The company's mission is to sell new radios. With the general bad reaction to the Extreme Upgrade's cost, I don't see Uniden sticking to that business model or busting their tails to add new features to existing products via paid update. And R&D still costs money. (Although that implication was loud-and-clear in the early HP marketing. I remember 'never obsolete' in there somewhere.) Uniden will probably maintain the databases for upload via Sentinel for both the HP and the new radios until the technology changes again. But, I'm confident that HP owners have seen their last firmware update. There's no escaping radio de jour.