If Renoise could sample what it was playing (e.g. a bass with effects and layering) and capture it as a new sample instrument, that would be highly useful for making thick basslines, leads, hoovers etc.
Also, the ability to layer two sample instruments together into a single new sample instrument at the click of a button would be utterly awesome. Because of the integrated sampler and audio editor, Renoise can take away the messing around involved in bouncing down samples by doing it internally, allowing for all sorts of audio alchemy to easily occur - please consider.