Fergus, I downloaded the ZoG implementation and tried it. But it's obvious from the design that the branching factor is humongous. The pawns in chess have a calming effect on the game, like the control rods in a nuclear reactor. Without them an explosion results. Instead of pawns you have inserted pieces that do the opposite, increase the confusion. There is no strategy in this game, it's plain mayhem. Of course, it could work as an illustration of overkill in chess variant design. I am not against that you try out new ideas, but sometimes the result is a failure.
/Mats