I think that a custom solution that sits on top of pip might make sense. Not in the immediate future, but long-term. In a lot of cases, iOS needs to be special-cased, and it's quite common that a few files have to be patched to get some packages working in Pythonista. I'm thinking of something like a curated directory that's based on whitelisting pypi packages and in some cases hosting patches.
To be clear though, those are just some ideas, not something I'm actively working on at the moment.