I don't think open source is the particular answer to the problem you state, I think it's an orthogonal issue.

If you have millions of users who want to ask questions (think of supporting Microsoft Office), then direct access to developers is a non-starter.

What I have seen work are rotation programs where developers spend some time as first-line support (maybe 1 week per year). When doing so, they help educate the rest of the support staff, and they get great exposure to real users facing real problems.