Kolla, you say that as if you know for sure, but you're just making it up. You don't know if an Amiga "app store" would be a failure, but you seem like you don't want us to try.
This is a very common attitude here. "You can't do this" "Don't even bother trying" "I know everything, and I say it's a bad idea"
What are you trying to accomplish by preventing us from forming ideas that could help us develop a new software distribution and advertising method for Amiga platforms? Why does it have to cost so much to set up such a system? How many developers have you asked who have said they wouldn't be interested in a better way for their product to reach its target audience?
We are seeing new users signing up on Amiga forums every week, either coming back to the computer system they love, or trying it out for the first time. Many are finding out about Amiga through YouTube where they see Amigas running software they never assumed they could run. Lots of people are starting to prefer using pre-installed Workbench packs like AmigaSys, ClassicWB and AmiKit. You can't see the potential that including this "app store" in these packs could have?
The applications included in the store don't all have to be new and current. We could include good software that is already available, essential shareware that's been around for a while and still requires registration to get the most out of (MUI, WHDLoad), shareware that's still in development and isn't hosted on Aminet (SabreMSN, AmiGift), commercial software and games whose authors are searching for an Amiga-based distribution method (Babylonian Twins), or software that hasn't been developed for a little while, but is still not available on Aminet (AmiNetRadio, Dynamite). Hosting software like this might stir up new interest in it and maybe even convince the authors to come back and update their programs, or open source them. I'm pretty sure a lot of Amiga users aren't as aware about how much good, recent software really is out there, because there's just no easy way for them to see what's available. Browsing Aminet's recent page only shows what's been released in the last couple of weeks, but after that it goes unnoticed unless someone goes searching for it.
I think Ubuntu's Software Center is an alright example of an online marketplace/app store, although I would prefer to have user ratings and reviews, and of course the ability to purchase or register software directly through the program if it's required.
I hope more people can help contribute positively to this thread instead of trying to drag it down and prevent the Amiga platform from progressing and evolving.