From a security perspective perhaps it's not that interesting-- although signing oracles are all too common access to one is already close enough to a total break even before getting to the padding restriction. (e.g. go ahead and sign post dated certificates too).

But the technique is interesting as an object of study, in a way that finding "beginner-levle crypto misuse" absolutely wouldn't be, so it makes it more relevant as an academic publication. It further clarifies just how fragile these constructs are.

Also from a security perspective I suspect this may be a total break on some blind signature token schemes that use RSA. I've seen some of those avoid using ECC on the basis of the complexity required to avoid one-more-signature attacks that require making a fair number of concurrent blind signatures. (and have a shape a lot like this attack!)

> How do you fix a "vulnerability" that doesn't exist?

Don't make a signing oracle (esp one that doesn't even do the padding itself) available!