Just my OS X centric opinion once again because I think that, in this domain, Mac OS X/Cocoa gets it nearly as right as possible. Font management is done at the OS level and every Cocoa application (Cocoa on Mac OS X = GTK or KDE on Linux) gets for free:
I have to say "wow". I dont know what systems OSX uses, I imagine it's not fontconfig but rather Apples' proprietary and patented font stuff. I could be wrong.
Still, I think that a very minimum level of font "filtering" should be a priority for the various GUIs under Gnu/Linux because apps like Inkscape and Blender and Gimp and Scribus are starting to make it a real designer's platform.
Fonty Python sounds a little like "Font Book" in function. Perhaps not as sophisticated, but it's aim is to put *only* the fonts a designer wants into their user zone. Ideally, design programs (or their gui toolkits) should respect that and allow the user to *at a minimum* filter the view and see *only* their user-zone fonts.
Thanks for the insights, /d