The question isn’t so much as to what utilities that Día uses, nor what platform is managing the code.
The discussion should be about is there anyone that wants to maintain Dia for Windows, and who is prepared to maintain Día for Linux.
Also, you are forgetting the Mac binaries. Although the MacPorts version works flawlessly at least up to High Sierra. Not sure who maintains the MacPorts version but it could be derived from the FreeBSD ports (not sure), and these distros are compiled so they are generally easier to maintain that installable binaries.
Linux versions would be generally no-issue since they are mostly maintained by the two main distribution sources: RPM and DEB.
Until those to questions are answered, any other discussion is academic.
Disagree. I don't think that maintaining the Windows and Mac binaries solves the underlying problem here. Maintaining those binaries is probably very tedious and people will avoid this like the plague. Precisely the problem is aging technology (e.g. GTK2) that may eventually prove impossible to maintain.
