Adding more mine levels After 9 they slowly unlock forever.
This would remove the need for a world reset caused by mining limitations such as finding good feldspar for clay for anvils..As over time the deeper we go the better the stones/ore/feldspar we could attain. We have a catch-up 24-hour mechanic on placing mine holes after someone reaches that level.
A scaling factor would be best starting at 1 month for 10-15 then 2 months for each level from 15-20 etc.