> That’s wrong. Data protection legislation expressly forbids
I'm sorry, I assume that English is not your first language. 'Can' means 'is able to'; 'may' means 'is allowed to.' The GDPR does not allow selling something, but it's still perfectly possible for someone to do so. People break the law all the time.
I raised the issue of can vs. may because it's germane to the issue of immutability. It is possible to build a system in which it is mathematically impossible (within arbitrarily-determined limits) to alter data; it is not possible to design a system in which it is possible to prevent someone from telling someone else something he knows. It's odd to me that the GDPR bans the former, desirable system.
GDPR has expectations that Data Controllers take reasonable steps to protect a data subject. Theres no expectation that you anticipate all mathematical possibilities...
It allows for simple logs. It does not allow for simple immutable logs, because your customers must always be able to force you to forget about them. There's nothing about sharing data between organisations: the GDPR requires — with certain very minor exceptions — that someone holding personally-identifying information delete it on request.
As an aside, this:
> This actually enables further innovations for instance you can log a cars behaviour without a user fearing you might sell this information on to their insurance company.
… isn't really true: the logger can still sell it, it just may not.