Are you planning to add touch bar support for the MacBook Pro in the future?
Geany uses the GTK library for its GUI and input handling and this library is primarily for linux; the Mac port isn't maintained very actively and unless someone adds support there, it won't be possible to add the support for Geany. I don't expect it any time soon.
Just curious - how does the touch bar behave now with Geany? Is it possible to at least show the function keys and do they work?