The Flatpak is already packaged and works well. It just needs to be maintained from a person that joins the Inkscape community.
This would allow further improvements like Portal support and making the app official on Flathub.
Update: One might have been found!
(except snap, but they seem too Ubuntu specific).
For what it is worth you can install Snap on most distros. https://snapcraft.io/docs/installing-snapd
Not officially but people have managed to reverse engineer it before in order to host their own - https://forum.snapcraft.io/t/lol-an-open-source-snap-server-implementation/27109
Whilst I do get the sentiment (and in no way do I support Canonical in keeping it proprietary), how likely is it that alternative Snap repos are going to show up if they did make it possible? Even with Flatpak where it is encouraged and documented I don’t think I’ve heard of anyone setting up a Flathub alternative of any significance.
elementary has their own repo for their system apps
I didn’t know about the self-hosted snap stores, thanks for pointing it out!
For what it is worth you can install Snap on most distros. https://snapcraft.io/docs/installing-snapd
Snap is a cesspool for malware and shovel ware. The best apps are packaged by Canonical. Also, when people still cared about Snap, there were frequent reports of incompatibilities because it was developed with Ubuntu in mind.