I have a file that I built in version 8.5 that gets custom functions from 2 different sites, plus it has a table in the file where I can save all my functions as well. I find it to be a little bit of a pain in the neck to have to import functions from one file to another. Remembering what file I had that function in, is sometimes not always an easy task.
My file has an option to copy the custom function to the clipboard. Since the only Open command that is not available in script workspace is Open Custom Functions. It is a little frustrating to Copy Function form table / Go to file that needs function / Open Manage Custom Functions / Create a new function / paste form clipboard to function area / enter name, parameters, function / close new function
If we were able to have a table(s) such as I have and with New command Open Custom Functions. We could then create a new function by entering the custom function ID from the table and it would and the name, parameters and function calculation would auto fill from related function.
So in closing you could save a custom functions table as a template for future files, and to create a new function would be as easy as explained above.