I recently played a DBA24 game using 24 elements per side and one pip die. The single pip forces you to group most of your troops and use group moves. An enjoyable game & plan to do more. Using 21 elements per side with 9ne pip die should work the same way.
A little off topic but the one and only Tony Aguilar just unboxed a book on 16th century warfare on his youtube channel. He mentioned bringing DB-RRR up to 3.0, which would be very interesting, especially as Eureka have just released an 18mm ECW range.