Forum-specific themes? Group-based theme permissions?

Howabout the ability to set a specific theme/skin within a forum? like have a theme hidden from regular use but let it be used for a specific set of forums on a board?

to expand on this idea further, can we have it so there's a group permissions section for themes? So which groups can see/use a theme, etc.

This would be helpful for account upgrades for say a premium membership gets access to a different theme regular members cannot use?