Before you will release Renoise 3.1 soon, please consider changing the ratio range of the compressor and bus compressor so it starts from 0,2 for using it as an expander.
Or if you planning to add a new compressor, please consider add the expander ratio to this new device.
An expander ratio / device can be very useful, for example if you use a preset sound from a synth which uses internal dynamics and quickly want to decompress it without loosing the overall sound.