I'll judge FR5.1 to be valid.

It's consistent with itself and earlier-posted fantasy rules, as it is written in narrative form, which now seems to be a real restriction instead of a theoretical one. It's also consistent with the regular rules and has been posted properly for the current round. It does make an assertion about later FRs, but there's no reason this should be the last valid FR of the round.

Therefore, it's valid.

Very clever, themink!