With multiple app stores, developers may not release to the Apple app store any more. Causing users to either use other app stores or miss out on apps that would previously been in the Apple store.
Causing them to be forced to evaluate the trustworthiness of each new app store they have to use.
Which will inevitably lead to some less tech savvy users having their information phished out from their phones.
Personally, it sounds like a hassle to me. I’m a big fan of the walled garden approach because I have zero desire to evaluate app store’s credibility and don’t feel I’m missing out on anything that could be side loaded, but then again, I only use my phone for communication, dating, photos, craigslist, and hackernews lately.