Alright after looking it up a bit, some things I noticed. Mostly taken from the 3DS trailer in the E3 direct (and a couple daily pics):
1. The background doesn't seem to change between the menus accessed from the main menu (but does seem to be repositioned when banners are added to the top of the screen):
But it does for some submenus elsewhere:
2. The menu is not uniform with UI elements. Buttons are inconsistent in design and layout a clean swap even in continued selections tree, from what we can see. It's actually kind of weird that this customizations menu looks identical to a submenu of online play. The bottom banner from the Nintendo Network menu has only officially been shown there so far, no other menu screens seem to have it (but we have very few that are shown on the top screen):
3. If real, this would be the only menu so far to actually share a design with another, but so far they all serve radically different functions of the game and uniformity probably wouldn't be expected anyway.
4. None of this is intended to prove or disprove anything, in any case.