For Slackware -current users, I made a new slackbuild of Flatpak 1.4. I also went through and updated every dependency to its latest, adding several new ones in the process.
If anyone would like to test it, you can download the tree from my github repo
https://github.com/afhpayne/flatpak_slackbuild. If you hit trouble, let me know or do a PR.
Happy slacking.
