Keyboard music often requires more than two staves - AFAIK the greatest number used by in a composer’s autograph (and for good reasons of clarity) has been 11 in a large scale work for organ, though a published edition has condensed that to number to about 5 or 6.
In these situations one does not necessarily want the same number of staves on every system, and there may be no “underlying logic” to which notes are on which staves, beyond the requirement to make the score as readable as possible.
Even for a simple 2-staff piano part, there must be some method to assign the notes to the individual staves - not to mention cross-staff beaming and slurs, cross-stemmed chords (a single chord with notes on more than one staff), etc.
How do these sort of issues for keyboard notation map onto the “players holding instruments” model in Dorico? The examples discussed so far seem to be mainly about doubling by orchestral or band players.