I had, but the whole "relocation" confused me a bit My testing was inconclusive previously. I've fiddled around and am posting my findings here for other, so there is an answer to these specific questions, though once you understand the relocate it seems rather obvious.
Assuming that I have a menu module and some other modules in "inset" and the mobile layout is triggered, is only the menu module displayed? It appears that they all do if they are displayed on the menu item being displayed.
What if I have multiple menu modules - will they all display? yes.
What happens to the non-menu-modules that were targeted to the inset area? It appears that they all do.
I'm not sure why I struggled before.