I need to play with this. It's quite an idea.
I wonder if the King shouldn't be like any other piece, even in check; if
you're in check, have no card to move the King, and can't defeat the check
otherwise it is mate.
The concept will map with interesting results to a lot of variants that
use the ordinary 8x8 and 32 pieces. The cards might even work best with a
form other than orthochess.
Peter, you think too much! :)