Twisted Elevator Chess is a fine idea; and the name Twisted avoids the
nerdy connnotations of Helical. Note that a B going up one board changes
color, but regains its normal color if it returns to its original board.
Clearance by elevator is something I didn't think of, but it's a fine
tactical element, and also perhaps a nice problem theme on the two-board
game.
Hilarity by express elevator might work, but I doubt it. The only fair way
is to first announce to which board the piece is going (perhaps blindly)
and then get up from your seat with the clock running and carry it there.
If a collision occurs, same rule as always, you walk back to your own board
and replace the piece and then are free to make any. Express could pass
through blocked levels?
Or had you pictured the mechanics of express more like this: the player
picks up the piece, screams 'EXPRESS!!!', and then throws the piece in the
general direction of a teammate?