If there are, say, ten thousand license plates of interest at any given time (which seems high), that’s what, 10KB? Not really that hard to update that every 15 minutes (or hell, every minute).

I don’t really see any drawbacks with storing them on the device, they should already be quasi-public knowledge (from warrants/etc) so it’s not like there’s a privacy/security risk there

There is a meaningful value in catching stolen vehicles and child abductors. Not high enough to justify capturing every single plate, but there's a value.

Bear in mind this is not meaningfully different than previous mechanisms of issuing BOLOs. Law enforcement widely distributes information about plates of interest. In my area, those plates are often on digital billboards already.