Usermenu with submenu structure at dropdown field

Right now, no. The Account menu feature currently will only show the menu items in one level, even if some options are nested. The idea isn't to be a full blown 'menu module', but a quick way for a few user-specific links to be added to your site. A multi-level system has a lot more requirements on styling and functionality, and would be very difficult to implement properly in the drop-down in a way that would work on multiple templates.

I can see adding a multi-level menu system in the future, but we don't have any timeline on when, or if, that would be implemented.

I hope that helps explain a bit more, even if it's not what you were looking to hear.

Thanks,
Alex