Yeah, it's a website for an artist's association which include a gallery space. The editor for all the pages concerning the association and the editor for the subpage concerning the gallery space are not the same.
But the super Admin, myself , is able to edit everything at once with just one login and setup. That's the idea.
Work in progress means, it would be possible in the future?
Thanks for the multi-site setup but I'd rather skip this option for now.