@paidhi "somebodys" got to create a pull request to show it works, and given (almost?) none of the Geany devs use non-GTK based distros its probably unlikely to be them.
They also need to address the point @b4n made above, Geany adds functionality to the file chooser to provide a filter based on Geany filetypes, the ability to select the encoding to be used to open the file, and the ability to choose the filetype to use for the file (important if auto detection is wrong). AFAIK those can't be added to native filechoosers.