It’s super-easy to register, but it is only attached to your NNID. Who knows if this will actually connect in any way to your past Club Nintendo stuff, which would be nice to see your loyalty to Nintendo and its program(s). Since your Club Nintendo account was connected to your NNID, I’m sure there could be a way to connect them all for records, but knowing Nintendo, that’s not happening. haha.
It was still a painless procedure, so don’t worry about this taking more than 3 minutes to complete. Longest part was waiting for the code in my email.