From what I remember:

You can do pretty much what you want in a drivechain, similar to what you see in the ETH L2 world at the moment. From optimism, zk rollups, zkevm, etc.

It allows to keep a state in another chain anquored to L1.

Security is via time delayed changes in L1.

The changes to L1 btc would be minimal and do not change what already exists.