Since pamac currently does not integrate with Flatpak, I have decided to create a Flatpak management GUI (I did not know the right category to post this, so I am writing here). I have just released the first version (0.1.0) in AUR as fpakman. At the moment it has a tray icon (that gets red when new updates are available), and a management panel (where you can see the applications/ libraries and update them). I planning to allow search, installation and deletion for the next releases. Also the possibility of downgrade applications versions.
The current AUR installation does not put the app in "autostart" mode, so you have to register via your Desktop Environment settings or terminal.
I hope this initiative can help other people wanting the same features for their system.
Suggestions, translations (the first version only supports English, Portuguese and Spanish), and pull requests are very welcome. The GitHub project link: https://github.com/vinifmor/fpakman