@tisto There are two ideas.
- One is to give the themer the mecahnism to have two themes. One for CMSUI and one for public pages. And the public pages theme would only have to include the barest minimum CSS/JS to get the toolbar visible and nothing else. The toolbar was built to use very little specific CSS anyway.
- take this further and put the toolbar into an iframe so there is no need for even the minimal CSS being included in the public theme.
Option 1 was implemented by me and is in the core. Option 2 was tried by Rok but he gave up. Mainly because we was trying to do even more which is create all the CMSUI as popups originating from inside the toolbar iframe. Which wasn't really needed in practice. It's not that bad just reloading the page on a toolbar click.
I had assumed the new volto theme separation feature was more like option 1 but are you saying iframes are used so the toolbar shown on public pages is completely isolated from the public theme and no inclusion of any min js or css is required in the public theme? If so thats great. It will reduce the cost of theming enormously.