I think the international "rules" are >140 UTQG. I don't think a blanket tyre rule is the best answer but it's certainly a lot simpler than some of the other ideas going round. Simple is best.
I'm sure Russ values the opinions posted here but it is his series and I'm pretty sure he has a set of rules in mind which will be made available as soon as they are finalised. People then have a choice, run within the rules or don't run.