Is it possible to use a track as recording source (track to track routing) for purposes such as resampling?
For resampling: from a right click menu, you can render to sample selection, column, track, group, or pattern. Renoise will automatically create a new instrument with the sample, with which you can do as you please.
Would be nice if one could resample while playing live though.
Exactly what this guy said. I intentionally left out “so that i can do live automation etc” to see who would just say “render”. 
Anyway thanks… any more ideas?