The issue I would have of organizers filtering the questions is that will the organizers give more to their friends over the the rest of the community?

A lot of the WordCamps and meetups are usually the same rotating people around that are friends with the organizers.

Now yes there should be a sort of filter so the same questions don’t get asked again and again.

There is a disadvtange of e-mailing or whatever the speaker after their session, what if the speaker wants to see another speaker?

Just enforce a rule that you can’t just ask your question to promote yourself/your business/etc…