One thing I disagree with Ultima (and Rococo or Maxima) is the presence of
two Long Leapers and one Withdrawer, because a Long Leaper is even
stronger than an Advancer. The Immobilizer and Pincer Pawns are also too
strong, (Maxima demotes them slightly.) As for the Coordinator, I am not
so sure.
In that respect, Chess is very balanced.
(2 Knights are slightly inferior to 2 Bishops, which are slightly inferior
to 8 Pawns, which are slightly inferior to 1 Queen, which is slightly
inferior to 2 Rooks.)
I would suggest to use a King, a Withdrawer, an orthogonal Coordinator, an
orthogonal Immobilizer, two diagonal Chameleons, two Leapers capturing
like the Knights in Peter Aronson's Jumping Chess, and eight Pincer Pawns
moving one square forward (two if they are on their starting position).
Castling, promotion (as is already the case in Rococo) and en passant are
back. The Immobilizer and the Chameleon still immobilize all adjacent
pieces, but the Chameleon captures a Pincer Pawn with a diagonal move.
Maybe adding one or two Advancers in hand (perhaps moving like a King)
would constitute a good subvariant.