"People know what they want, but people also want what they don't know." - Gilberto Gil
People know what they want- when they see it.
They may not be very good at telling you where their itch/pain is out of the blue. They may be taking it for granted and not even feeling it anymore. But if you just start scratching/massaging _somewhere_, you'll get useful "more to the left, no, a bit more up- THERE- AAaaaahh!" feedback. If you're so out of touch that they will push you away rather than steer you into the right spots, well, that's useful info too.
I don't imagine that feedback will be coming easy unless there's the prospect of an almost immediate solution (I'm less likely to discuss back itches on the phone). Your idea, as I understand it, offers a slim chance that each specific problem will be addressed, and even in that case the solution is months away.
Filtering people out isn't necessarily bad. This may help in identifying problems that hurt a lot. What you probably want, though, is problems that hurt lots of people.
Having something like what you propose would be better than not having it, and I don't want to discourage you from the idea. Just don't expect it to replace "trying to guess what many people would want."