I'd like to jot notes about users I add, such as kinks, limits, or even SFW interests.

I currently can only do so via nicknames, and think having a summary section per friend would be nice.

If the db is relational,  then all we would need would be a text column in the same table/service as nicknames.

If the db is no-sql, I am not as sure of implementation, but I imagine all it would take would be to just add another field...