Hi,
Not going into the discussion if there actually is a “gap” to be filled (most DJs that play requests don’t want to advertise the fact, let alone actively stimulate requests. You’ll end up jukeboxing requests all night. Also people will ask for what they know well, thus limiting the possibility for the DJ to introduce new music.
Perhaps an alternative idea is a “voting” system, where people can vote for the current track and perhaps indicate they want “more of the same genre”, “faster” “slower”, “different genre”. It would provide the DJ with direct, real-time feedback on what the crowd is doing.
I am pretty sure there is not gap for that either, but perhaps some DJs would find that kind of information handy in programming their sets.