Are you trying to make these identities to be firewalled from each other? i.e., do you not want your family to know that you go by "Master Dan" in certain BDSM

Are you trying to make these identities to be firewalled from each other? i.e., do you not want your family to know that you go by "Master Dan" in certain BDSM communities? Or for someone who is transgener, but isn't yet ready to let a set of friends/family/coworkers know yet by the choice of a differently-gendered name? It turns out this is extraordinarily difficult, and if users think they can maintain this separation using a single account, and then they get burned, they are very likely to blame the social network involved. Which is a pretty good reason why the architects at FB or G+ would probably think very, very carefully before implementing such a feature.