I just discovered your binding as I was considering starting my own development. I think it pretty much supports my needs (presence detection).
I installed your binding and tried to configure it - it works just fine on Unifi Controller 5.4.11.
I have a few ideas on how presence detection could be improved:
You could considder adding the following bridges
A specialized "Presence Bridge", The primarily use of that bridge is pretty much what you already are doing presence detection. The bridge should come in two or three flavours: One representing the controller and one a AP, the last one could represent a person (as a person could have many devices).
The thing should be the client that you already has created.
There should be a property on each bridge telling if some of the clients monitored in openHAB is Online. The presence detection is then done at Bridge level, and you have the possibility to monitor a room (if you have enough AP's) a location or just track a persons presence.
Version 2 would be to add some probability calculation to determine the probability if a person is present. As an example we have a tablet that we use as "remote" for our ChromeCast. It is primarily my wife and one of the kids that uses this tablet. So it would be obvious to use that tablet to determine who is at home. Since the tablet is always present, it would be relevant to check if it is transfering data. Sometime ago I stumpled over a article about that topic, and it seems quite interesting (although it is complex).
Just my thoughts, I would be happy helping, I have just finished first version of the ZoneMidner Binding, so I have a little experience in openHAB 2 Bindings, though my Java experience is very limited.