Regarding MUI, if its becomes a part of the requirement of the low end AmigaStore, then either;
1) Include MUI in the install archive of the Store
2) Make it very clear, with instruction where to find it and how to use/install it
MUI is "standard" for old users, but for returning people like myself when a program refuses to run because it wants xyz file/program as a basis, its not as apparent where and how to go about it.
Going to OSdepot or Aminet you have tons of directories and subdirectories. If you know the name or close to it, you can search, only to find 10 files with similar names etc.
People usually figure it out by asking around on forums, but why not make;
"Installing stuff on amiga for dummies" a standard assumption when making programs

Idiegogo storefront PDF that Pascal just posted was an excellent example about how instructions should be made.
This is not just a comment regarding AmigaStore, but more in general

Ofcourse, Epsilons blog have kinda set the standard in that regard.