So, about backup loading.
(Don't take anything I say as facts, I'm not involved in any technical stuff due to lack of time and skill)
Hekate (which conseguently uses a stripped down version of Atmosphére) supports
exeFS redirection (which is used to load hbmenu) in a quite simple manner:
you just create on your SD a folder called atmosphere/titles/TITLEID/exefs and put your 'main' and 'main.npdm' inside.
(Here's a list of titleIDs
http://switchbrew.org/index.php?title=Title_list/Games)
You can do this with any title (including game cartridge).
Out of curiosity I attempted to load Zelda:BotW exeFS with this method and it did indeed load (or I think it did) just to crash soon after saying that "The software has been closed".
What of course we are missing (or I think we are) is romFS redirection (which was implemented in one of the latest Atmosphére commits).
If anyone wants to play with this, be my guest.
(Once again, I feel to need to reiterate that I could be, and probably am, wrong.)