This is a good idea in principle.
I don't see any need for a new setting. Different icons are just better. It would be a setting you never want to turn off, and unnecessary settings are just bad usability.
If possible, the icons should be configurable, and managed using the same screen where you manage the other file type icons.
The only difficulty I see is that for other file types, the icons are controlled just by the file extension. Here you would need to look at more of the URL. I don't know if the current API extends naturally to handle that, I have not looked.
Note that the current API does use the file extension to determine the icon. For example if you like to http://example.com/file.pdf you get a pdf icon. This is good. I think that even after your change, if you like to https://drive.google.com/file.pdf, it should be a PDF icon. It should only be a Google doc, or Google spreadsheet icon, if you are linking to one of those.
Thanks for working on this.