Heya,
I would like to propose an on_avatar_entry/exit event.
Some systems like the medic system care about an avatar entering or exiting a region to keep a list up to date or to rez/derez things.
While I am aware we can use agentlists, this is more inefficient to run every minute or so to update a list. Especially when dealing with large amounts of avatars in event spaces, as this will take a lot of memory.
This allows for a more passive than active system, causing less load on the region especially if list operations get involved.