modulus

I can think of alternatives. For example, the server could keep the user’s private key, encrypted with a passphrase that the user must have. So key loss wouldn’t be an issue. (Yes, passphrase loss might, but there are lots of ways to keep those safely already, compared to key material which is difficult to handle.)

I generally agree, though I could be convinced of recurring payment in the case of high speed APIs that need a lot of updates to keep working. Chasing an API can be a lot of work.

Of course, a solution to that is having an up-front payment and letting people update as they wish–if there’s new value in the new releases presumably they will.