If we get iOS system or full icon theming (which I can almost guarantee we won't) - it'll be a hot effing mess if Apple doesn't gatekeep it hard. I was heavily into the Cydia theming scene back in the day from iPhone 3G to 6S, and there were so many awful themes out there, alongside very well-done themes (the ones which weren't clipart with a rounded square mask, lol). Perhaps the dev program will be a requirement, and that small cost will keep most low-effort content out.