>> Yes, something that easy (or even easier!) is possible with an X 
>> terminal. But it's an unusual requirement (most people use a single X 
>> terminal)
>
> [citation needed].
>
> People use multiple workspaces/virtual desktops on a single X display, 
> multiple windows on a workspace, some of those windows are terminal 
> emulators, some terminal emulators support multiple tabs and/or panes, 
> and people use those.
>

[citation needed] 😉

>
> So:
>
> * One can switch from an X display to a Linux TTY with Ctrl+Alt+F[1-6], 
> and back to X with Alt+F7 (usually).
>
> * One can switch workspaces with a mouse click or a configurable set of 
> keys.
>
> * One can cycle windows in a single workspace with [Shift+]Alt+Tab or a 
> mouse click.
>
> * One can cycle tabs in a single window with an application-specific 
> shortcut or a mouse click.
>

All that is nice, but it's not what Richard asked AFAIU.  He comes from a 
multiple terminal background, each of which is completely separated from 
the other ones, and what comes closest to that is to have multiple X 
servers running in parallel, and switching between them with, say, M-F<n>. 
At least, that's how I understood his question.