The ability to add/edit comments for a translation would be useful - has anyone looked at this?

Comments

Where do you imagine that would be stored / shown?

Stored in the pot file (///), shown in the interface.

Localization client saves data into the local (and possibly the remote localization server) database. Neither of these two have ways to add comments for submitted translations as of now. So this would be somewhat of a bigger development. I'm not sure about the usefulness though (although the server has an issue in progress to add comments for translations, but that is going in different ways and will probably not let remote comment submission really). Even then it would not be possible to save locale as it works now.