I will share something in the coming days. But in essence, I changed on the host color scheme, font size, scaling factor in the Plasma desktop, etc, and in most cases, there are differences between the traditional apps and the snaps.
I understand that there can be conflicts, but we can think of elegant ways of solving those that do not require user interaction. For that matter, we can “mount” themes from any gnome version - so the snap thinks it’s the real /usr/share/theme - we just provide all of the content to any snap with or without the explicit extensions declaration.
I’ll come back with more details, especially for HD displays, and a suggestion for implementation.