It is actually possible to attach a microcontroller to the Bangle's SWD pins and to use that to communicate, so with a small PCB with a light sensor and a cheap micro you could communicate that info back to Bangle.js.
... but yes, I think if a Bangle.js 3 was done such that it could be opened I'd definitely add some spare IO so extra sensors/etc could be added. Realistically for something like light you'd need to modify the case 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.
It is actually possible to attach a microcontroller to the Bangle's SWD pins and to use that to communicate, so with a small PCB with a light sensor and a cheap micro you could communicate that info back to Bangle.js.
... but yes, I think if a Bangle.js 3 was done such that it could be opened I'd definitely add some spare IO so extra sensors/etc could be added. Realistically for something like light you'd need to modify the case though.