I've thought about this a bit. And I am rather of the opinion that the preseed can go away. Originally we introduced it as a stop-gap because snapd didn't know how to install content snaps automatically, now it does. On top of that was the appeal of having the snaps be cheaper, but, in reality they aren't really, you just happen to download it along with the ISO. Now while that certainly does make sense to a degree it's also somewhat silly to only preseed the content snap itself, instead I'd much rather have preseeded applications be snaps. As it stands right now the preseed serves no actual purpose anymore and should be removed. If and when it makes a return I'd think it would be in the form of application dependency.

Also, since I am musing on it already, the same goes for the flatpak runtime really. If we want a runtime on the ISO it should have valued through an application, not lend value to the application being cheaper to install.