Hello!
Note that the original plan was about GTK#, not GTK, therefore Eddie's GUI would have remained anyway based on Mono..
All the AirVPN Suite for Linux and Hummingbird for Mac were born to provide a software completely unrelated to Mono. In Linux you also have a real daemon, Bluetit, capable to offer a strong basis to develop any AirVPN client, even from third-party developers. In the past third-party AirVPN clients developers faced the formidable barrier of the undocumented bootstrap servers and undocumented "manifest" file format. No more problems of that kind now, as you probably know if you have checked Bluetit developer's manual.
Kind regards