[IanCal]

Now this is some good nerd sniping content.

A few quick thoughts.

You could have a move counter, and pick representations based on total moves (early on, you could probably use lots less space simply storing the movement from original position and piece type).

Bishops can only be in one of 32 spots but you need to know which one (ordering?).

Trying to not shave off bits but have more zeros so that it can be compressed more effectively - having positions based on the delta from their most likely position could help.

[thrw21]

  Bishops can only be in one of 32 spots but you need to know which one (ordering?).

I was thinking of that but piece type is already 2 bits for 4 piece types so you can't have unique color bishop types without adding additional bits. Ordering wouldn't work since you can only have one bishop or an extra one or two of same color etc.