HaikuDepot is fine, but I can see why people might get confused at first. I myself was a bit lost on the first 20min of use or so 
Nowadays, the “store” concept is widely used in all types of OS: we have Google’s Play Store, Apple’s AppStore, Microsoft Store, Steam store etc. The idea of catering to the world with an already known concept seems appealing indeed, but at the same time “losing to the establishment” feels somewhat wrong doesn’t it?
I think there’s a simpler way: A dialog/assistant on 1st boot that points the user on the right track. This is the Tracker, it does this and that. This is your home folder. This is HaikuDepot where you can get new software.