I can’t say whether opening the tire rules will add entries, but I can point to examples where tightening the tire rules directly resulted in lost entries, going back 10 years and as recently as a week ago.
There are people who will race because they can run what they have, knowing full well it’s not the optimum package. And if I was told I could run any tire I wanted tomorrow, there’s one compound I’d order and go on my way to any track confidently. Ordering every tire under the sun is a ridiculous alternative to a little research and friendly discussion.
Spec tires help the organizers, not the competitors.