Is your feature request related to a problem? Please describe.
I usually use tabs as different projects, or specific UI layouts (eg: diffview, neogit, etc) and for that I remove the tabpages from sessionoptions, but then closing the tab leaves me with a lot of buffers related to that session open, which could be closed.
I know that plugins like https://github.com/xolox/vim-session#tab-scoped-sessions implement this feature, so I just thought that it would be very nice to have that as well :)