Active ISA would be a disaster. My fairly modern car is unable to reliably detect posted or implied speed limits. Sometimes it overshoots by more than double and sometimes it mandates more than 3/4 slower. The problem is the way it is and will have to be done is by means of optical detection. GPS speed measurement can also be surprisingly unreliable. Especially in underground settings like long pass-unders and tunnels.

If the system would be based on something reliable like local wireless communications between speed limit postings it would be a different issue - would also come with a significant risc of abuse though.

Also the passive ISA was the first thing I disabled. And I abide by posted speed limits.