Assets should have... CUSTOMIZATION of directories and subdirectories, apart from question of (also desirable) easy adding of assets. definitely...
only in assets window, maybe?
Perhaps it should read them off of an actual folder structure? (that you can tweak and move assets around in... only problem comes when models are updated )
Or perhaps you could add tags to an asset and filter by these tags? (this would allow a mass dump of assets and let models exist in multiple categories... but the existing filtering I think might need a bit of improvement.)
(It would be really useful to actually remember what the last asset highlighted was and what folder structure was expanded when the dialogue collapsed.)