Deckadance has a couple of useful features which you might want to consider adding to mixxx.
- start mark: this is like a normal hotcue, except when set, the song is loaded in future from the point given, and you can't go beyond this point in beginning of track (seek 0.0 point). When set, you never need to seek empty space from track start again, or look for the 'here starts the beat after 40 seconds of useless noise' point. You could always set a hotcue, this would be like fifth specialized hotcue with the 'load this with track' exception.
- leap: this is a variation of beatgrid loops, where the software keeps track of underlying audio: when you release the leap, the song continues from where it would have been if loop did not occur. Very useful if you want to for example repeat something three times and easily go back to beat without losing sync
Maybe some others, but these were my main thoughts when testing mixxx :)
Also, it would be nice to be able to store the time signature of song (4/4 by default) and show a 'bar start' marker in waveform matching this. Not really critical though.
Please file these as separate bugs. Bug #703585 covers the "leap" function you mention, so please vote for that.