Addon that shows closest enemy players?

[Feehza]

I'd love if there was an addon that showed the 5 closest enemy players (or those within range) along with their health and what they're casting. Is this type of addon possible even if not yet developed?

Dont know if it exist, but its possible.
You cant determine distance to enemy units, but you can check if spell X is in range to an enemy.
So read out combatlog events and check if these units are in range for a spell and display it in a frame.

There are some addons who already filter units from combatlog to display it in a frame. Vanaskos for example (Kill on sight addon).

Sometimes i think for such an addon for my own needs:
Search combatlog for activities of hostile healspells. If these casters are in range then display these in a frame.
Its possible.

Edit: Try out Vanaskos and play around with configuration. Maybe it works perfectly for you.