I would *love* it if the Dictionary Renderer symbology method supported Legends. I have a few Symbol Dictionaries that I use and I find that their usefulness is really diminished by the fact that they don't support legends. A new user requires an orientation or to be sent a copy of a hand-made legend.
The legend couldn't show all possible symbol combinations, but if the user could define which symbols to add to the legend this would make the Symbol Dictionaries that much more useful. The Dictionary Configuration JSON might contain a list of Symbol Keys which would used by the legend to render symbols, similar to the output of the standard Dictionary Script.
Anything that lets the Legend in ArcGIS Pro render symbols used in a Dictionary style package.