[vqmhsnhy] Causing more pawnless engames

Create a chess variant which causes more pawnless endgames to occur (very rare in orthodox chess), in particular to unleash more madness such as Bourzutschky and Konoval's 517-move KQNKRBN endgame.

(Conversely, out of curiosity, what is the longest forced win from a position that starts with only kings and pawns?  This should be easy to look up in a tablebase.  Are there more "interesting" ones than the longest?)

One possibility is the known variant Upside-down chess.   We probably wish to have promotion restrictions to avoid an excessive number of queens. 

Here are some ideas: A "font" provides all the available pieces to which a pawn may promote.

* The promotion "font" consists only of pieces the opponent has captured (easiest for a physical board and pieces).
* The promotion "font" consists only of pieces you have captured (Crazyhouse-like).
* The promotion "font" starts with 2 each of rook, knight, bishop, and queen (the pieces of one additional chess set per player including extra queens) and is not refilled with captures.  Maybe the second queen only becomes available in the unlikely event all 8 pawns promote.

Incidentally, Upside-down chess (not aiming for pawnless endgames) might have a better strategic component if all pawns started on the 5th rank instead of 7th, as there is more space for pieces to shuffle around in preparation for attack or defense.