I've found rio-calc to be really useful for raster algebra expressions. I've come up with a few additional functions that are useful in my workflow that seem to work well within rio-calc.
I'm certain, however, that I don't know how to introduce these functions into rio-calc without directly registering these functions with snuggs within calc.py (e.g. https://github.com/rasterio/rasterio/blob/master/rasterio/rio/calc.py#L159-L164).
Is there a plug-in way of extending rio-calc to bring in additional user-defined functions?