

dont collect it all to some central database but have everyone make their own for private use.
This is how it currently works, and it’s why I think Predator is a better alternative (as far as privacy goes) to traditional ALPR services. Everything Predator records is stored locally unless explicitly configured by the user to do something differently.
What use is it to regular people to track others licenceplates?
To be clear using the word “track” is a bit generous here. An individual user won’t have nearly enough data to have anything close to a comprehensive location history on any given vehicle. A Predator user might be able to say “I’ve passed this car 3 times in the past month” but not “This person leaves for work every day at 9am”.
Predator is designed primarily to make use of ‘hot-lists’ where only license plates in a specific list trigger alerts. For example, the US has a program called AMBER alerts, in which emergency alerts can be issued for missing children/kidnappings. These alerts often have license plates associated with them. A Predator user can add a plate from an AMBER alert to their hot-list, and then forget about it. Predator will silently scan license plates as they drive, and alert the driver if they find the vehicle. I think this is a way better alternative to government agencies covering an entire neighborhood in license plate cameras that feed everything to a centralized database.
the whole thing will likely just be taken from you by force if nothing else works
This seems unlikely to me. There are already established companies in the space who have zero issue with violating privacy (i.e. Flock ALPR and Axon). A malicious company or government entity is unlikely to willingly go after Predator, given that it goes out of its way to make mass surveillance difficult.
Surely someone who wants to centralize ALPR information will simply use a service that already supports that feature. It seems unlikely someone trying to conduct mass surveillance would chose to modify a product specifically designed to make that difficult when there are already dozens of services that support that natively.