This is why i had hopes for AI blockchains as the data and trained models or functional algorithms could be verifiably provable as increasing usability/productivity/efficiency etc. You could still say your device/robot didn't improve, but if you continued using the models or algorithms then that would be noticeable. You would have to know they were still being used though, so you would need a time-sensitive encryption that calls home to activate, and if used in multiple instances you'd know that too. But reverse engineering the encryption to get the secret sauce sounds like a workaround. It could be made difficult for average folk, but not impossible. The real advantage would be micro/nano-payments and fee-less transactions since the device is the "miner", ie. by not using BTC/ETH etc.

At the end of the day a subscription model is probably easier.