maybe just a way to connect a wire - headphone jack?
Infra-red RX and TX - then it could be used as a remote control as well
Outline for a LiPo charger IC - you can get LiPo coin cells
If I scrapped the JST connector (now there's a coin cell) I might be able to squeeze bluetooth in. Not sure if a coin cell would provide enough power for Bluetooth though.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Maybe also:
If I scrapped the JST connector (now there's a coin cell) I might be able to squeeze bluetooth in. Not sure if a coin cell would provide enough power for Bluetooth though.