Hi,
As Co-Admin on a FTB Bukkit server I found it always difficult tu limit the use of certain items like the Mining Laser or other mod functions. In my opinion, it would work a lot better if the mod authors would use some kind of permissions system. However, there is no universal permissions api forge mods could use.
So my suggestion would be: A Forge Permissions API. I thought about something like this:
If a mod wants to check a permission, it posts a PermissionEvent (containing the permission id and the player to check for) to a special permissions event bus. Subscribers to the event can now check whether the player has that permission and set the event's result accordingly.
Additionally, one could also post location-based permission event, so items like the Wand of Equal Trade would be limited to the user's own regions.
This api doesn't have to define an interface for modifying permissions, that's up to the implementors.
I think this should be in forge as it would encourage it's use. It's comparable to bukkit where there was a big chaos in permissions too until they included the unified permissions api.