Ah - thanks. Too bad - that would be nice.
In the meantime - I have found a convenient way to "work around" this issue - although its a couple steps (but not too much).
I have found that using
A-PDF Explorer to see what books I am about to add to Calibre - and it is perfect for being able to see those which have the metadata in the info fields already and those that don't. And so then separate them into two sets - and ADD them using the appropriate method to get that info in.
I think you might find - at least for PDFs - that this MAY be an option for what you are trying through file names to - although I have not found the best corresponding tool yet to SET the PDF data in batches first. But have been trying a few. I'll let you know if I come up with a good one. That way you could have the filename with all that metadata - be used to import those fields into the PDF file itself. (And you can set "custom" fields - not just the standard INFO ones - not certain how it can do more than those into Calibre - but I am about to try some ideas. Since I know that having the ISBN:XXXXXXX in the comments field - puts it into the isbn field in Calibre. Perhaps similarly - using that format for others FIELD

ATA - using Calibre's fields, in a list in that Comments field in the PDF, can do this for others. Then if I can find the ideal PDF batch metadata input tool - that would be even better depending on what you are trying to add via filename.
But certainly at least with Author, Title, Published Date ... and even ISBN - this is a possible option for you. I'll keep you up to date as I keep exploring this from this angle (for PDFs - not sure about tools for other formats). Because if you could first have the PDF fields updated from the filename - and then (so TWO steps) import using the FILE METADATA - you will have accomplished what I think you are seeking.