> What is the value of "guaranteed forward progress" if in practice that progress can be made arbitrarily slow?

You're not defending against a malicious actor here, it's (IMHO) to prevent people writing stupid BPF programs by accident. People don't write "make my system slow but not freeze" scripts by accident.

What you are basically suggesting is adding support for exceptions which would allow a BPF program to be aborted at any point. And every caller has to decide what to do with an OutOfInstructions exception. Given the opinion of exceptions in the rest of the kernel and the complexity isn't adds to e.g. C++, I can understand why they don't want to go that route.