Rigol can't ever stop these codes from working because they sell them as upgrades. They can't put out a firmware update that stops legitimate keys from working.
Well, in principle they could introduce a new, stronger coding scheme for the unlock codes, hoping that no one breaks that too soon, and offer a "trade-in" program for legitimate buyers of old unlock codes/options. But I agree that this is very unlikely to happen, given the hassle it would mean for Rigol (verifying proof of purchase for legitimate options) and for users (having to obtain new codes after a firmware update to get options back).
It could be done in an easier way, especially for new customers, however if they would do so, I guess people would stop buying this model and opt for a slightly better though a bit more expensive model.
The hack made Rigol famous and the current number one hobby scope. I don't know if it was on purpose or not, but that doesn't matter now. It was a good thing to happen to Rigol.
Also, for hobby use, it makes no difference if you hack your device or not, as most people weren't in the market for the expensive options anyway. They might however want to have those options at work and here most companies would not dare to hack their devices.
Regards