I already kind of do this at the local level, with my friends who are also customers, but it's more like them telling me what they want and then me trying to craft it. Lots of free samples involved, it can be challenging
(who'd have thunk there are so many ways to do grape bubblegum?), but it keeps me sharp and usually pays off with them eventually liking and buying what I made. It's not always fun to craft juice for one person's specific palate, especially if that palate is finicky, but it has its rewards.
None of them are DIYers though, wish I knew other DIYers locally. I don't know if I really have much desire or if there's any point to doing it long distance through the mail. I mean, I could just post a recipe and you-all could make it, critique it, and tell me how much it sucks right here on VU, without having to pay for shipping.