That’s unfortunate - the spec is quite clear that multiple types are permitted. But sure, I guess a boolean could work as well.
Hm I was not aware that the FEP process was that rigid. That seems undesirable? If we go with the boolean approach, the change would not even be breaking. Why aren’t FEPs versioned with semantic versioning, for instance? Then we could use 1.0.0 instead of “FINAL” and this extra enhancement on top could be version 1.1.0.