Similar to the serial LCD backpack, it would be nice to have a backpack that was just a shift register. You could retain all the direct control over the LCD, and be able to chain a bunch of extra stuff on the chain if you want.
Continuing on the thought, it would be cool if you had a bunch of products with similar breakouts/backpacks you could have a two connectors on each for easy daisy chains. [V+, gnd, cs, mosi, clk], then miso on the other connector. The connector could be the normal 2x3 male headers, for which you can buy the female counterpart for ribbon cables (like the 2x5 Pin IDC Ribbon Cable, but 2x3). The 6th pin could be a passthrough with a tap on the board for whatever the user wants to put on it.