As per python-discord/sir-lancebot#1074, we should add a CleanedTextOrReply converter which will allow an argument to be provided either by text, or by replying to a message (if an invocation has both then use the text).
There's currently no file for converters, so we'd need a new file -- either botcore/converters.py as per bot structure or botcore/utils/converters.py as per sir-lancebot structure.
I'd like to implement this myself.