Abderrahim Kitouni commented:
We already build the core apps in gnome-build-meta, and buildstream already supports generating flatpaks. Are there any obstacles to using buildstream for the flatpaks of the core apps?
As it stands now, we build everything assuming a /usr prefix, and flatpak apps need an /app prefix. So we need to build them twice. Another (small) inconvenience is that the flatpak buildstream plugin is kind of hard to use because one needs to write the metadata file manually.
Another option I'm starting to consider is to only build them as flatpaks (and preinstall them as flatpaks in our upcoming OS images). This seems the logical next step to me in the context of GNOME/gnome-build-meta#142