User defined runtime attributes in IB are great. We use them for font name and other handy things (like CALayer attributes for corner radius, shadows, etc).

A word of caution, though. Using key paths in your categories like "fontName" is pretty dangerous. Apple could add such a property, or your users could already have one on their object, that would cause problems. I would suggest including a prefix or suffix, e.g. "cvs_fontName" similar to three-letter-prefixing.

I'll second the mention about checking the release notes of the latest iOS/Xcode beta, for those who have access. Moarfonts seemed promising, but caused nothing but problems when we tried it.