I'm posting this in InDesign, but the implementation may be easier as a Cloud feature so that it would be viable through all the Adobe programs that heavily use font (Photoshop/Illustrator/InCopy/etc.)

I'd love the ability to add custom tags to my fonts that are personalized to my individual account, and the subsequent ability to filter fonts by my tags.

Example: I might tag several fonts that I purchased a license for only a specific client under their name (PrivateCo). I might also tag several different fonts I received from a client to do a marketing campaign for under their name (ClientLLC). That way I can remember that all those fonts should not be used for a third party's project that I'm working on (BigCorp).

With the addition of a filter, I could filter out (or in) fonts that are for specific clients and not worry about forgetting down the line that I should not use this specific subset of the Helvetica font because I received it for use with "ClientLLC"'s projects only.

I could also set things like your favorite go-to script fonts "favscripts," which would reduce hunt and peck time through the (seemingly) endless font drop-down while I'm trying to decide what script font best suits my project.

I like the idea of "tags" rather than a straight grouping function because that means I could add more than one tag to a font based on need (ie-"favscripts," "favhandwritten"), and then filter by whatever tag word best describes what I'm looking for.