Ship PostgreSQL as default database
Because SQLite (Django's default database) doesn't support concurrency, users face a "database locked error" from time to time. See repomaker#164 for more details.
One solution is to fix repomaker to only make one request at a time. However, this is not quite easy.
Another solution is to use a database that supports concurrency, like PostgreSQL or MySQL. The former seems to be more popular around Django, therefore I suggest to ship it with the Flatpak. The footprint is not all too big (20 MB), compared to the total download size of Repomaker's flatpak.
Two example flatpaks that ship PostgreSQL: