Seriously guys, this isn't that hard to fix.
A change can be made to the theming structure so that all GTK+ config files in each snap directory are linked to the user's to honor the theme. It doesn't even require each snap to be written differently. Just put it in the guidelines for developers to follow. In the meantime a separate snap daemon can be written to scan for independent GTK config files in snap directories and link them to the user's.
Seriously guys, this isn't that hard to fix.
A change can be made to the theming structure so that all GTK+ config files in each snap directory are linked to the user's to honor the theme. It doesn't even require each snap to be written differently. Just put it in the guidelines for developers to follow. In the meantime a separate snap daemon can be written to scan for independent GTK config files in snap directories and link them to the user's.