Just reposting here what I responded to thepeoplesguild below as another consideration:

"If all frays were wild, for example, then it doesn't really matter what you're playing, but modern card holders will have an advantage with the newer abilities that the old cards don't have and that will encourage people to buy. So having more wild frays would make more sense to me than having more modern, because you can still play in wild with a modern deck, but you can't play in modern with an older deck."

This might be an option to make it easier to fill frays