Expander in the future?

One of these?




There is a plug-in that you could try here:
dynamics.ny (2.84 KB)
This plug-in is very new, so no instructions yet.
Negative values for the “Expand / Compress” control give expansion. Positive values give compression, so that is the opposite way round to the DBX II 128.

Installation instructions are here: Missing features - Audacity Support