Why doesn't ManiaExchange have a betaarea like TMX? That would definitly attract some more mappers, because they would receive some feedback for their betas

If you don't know what the TMX TrackBeta Area is check this link.

/fredair.esu

Instead of a Beta Area, people can upload their maps as unreleased on the details page. That allows you to share and comment on the track without getting your map awarded. Once marked as released, all comments and replays are deleted, awards can be submitted and the track is listed in the 'Latest tracks'.

You can browse unfinished maps here. Note that you can't 'unrelease' a map which is already released. The only drawback is that all maps need to be validated and have their shadows computed. Still, this functionality is enough to not have a dedicated beta area.

There is no subforum for beta tracks, but it's no problem to share unfinished tracks in Your Tracks. I suppose a thread akin to The Track Review Thread would suit the idea of giving feedback to unfinished maps well.

Hope that helps