im working on getting information about this as well, it seems that rather than requiring an imperial title they need an imperial backstory/background, similar to the tribal requirement for wildspeaker tree, the problem is nothing specifies what backgrounds allow this, as opposed to tribal backstories being explicitly stated in their description as "unlocks natural meditation type". i like the idea of royal psychic trees but i really wish it was made clear what the prerequisites actually are, rather than a vague notion of "imperial".