I'll have to investigate this Photon. Our game is not as latency-critical, so AJAX will work, but I want to find new solutions for future games though.
I believe the multiplayer plugin is based on Socket.io, or a specialized version of it.
If you do manage to write a centralized multiplayer plugin Vallar , let me know! I will eventually build a centralized multiplayer plugin for Construct, but I need to finish this game first to free up the time to do that, lol.