Advanced permission support was/will be introduced in Custom Items 11, but it has its limitations. In particular, it misses permissions for equipping items and using items. Also, there is no way to share permissions between items. After some discussion, I got the following ideas to improve on this:

Users can define a list of (global) permissions. Each permission has a name and a set of actions. The initial actions will be:

• Attacking with a custom item in the main hand (or shooting with custom (cross)bows or throwing custom tridents)
• Breaking a block with a custom item in the main hand
• Holding some item in the off hand while holding a custom item in the main hand
• Having a custom item in your inventory
• Having a custom item in your hotbar

Each item has a set of associated permissions and, for each action, an integer that defines how many permissions from the set of permissions having that action players need in order to perform that action.