I wondered if some Y class brown dwarfs might actually be registered as RoguePlanet's, especially the ones that have nothing orbiting them. Unfortunately I've not come across one since 2.2 was released.
I know that Y is already a class, and
in the API "RoguePlanet" is an "Exotic", so perhaps they're not related. However, A, F, K and M are also already classes in the main sequence AND have exotic types that are shown in the API. I think that these exotic stars appear in GalMap as their spectral class (top right corner) and are shown as their exotic class in the popup dialogue for a system. In the Sysmap the star description is always of the exotic class. Please correct me if I'm wrong.
So, I know it's a long shot and highly unlikely (a million to one chance it might just work

) but perhaps us explorers have so far missed the RoguePlanet description in the Sysmap and in the Galmap popup...!
Alternatively, there's only one RoguePlanet currently in game and it's called Raxxla.