The point is the set of operations that needs to be handled is larger than a handful of generic operations, and adding a constrained version of every possible floating point operation is unsustainable.
We need that for any kind of strictfp->standard optimization. I think the more important part is knowing which intrinsic calls the verifier needs to enforce should be strictfp calls in strictfp function, which we could accomplish with some kind of fpenv access attribute (which as an added bonus would help us rewrite strictfp functions)