I'm interested in making something for my Pebble as well, but am hoping to avoid C and use something like Kotlin Native or use it as an excuse to finally learn Rust.
Rust might be possible, but Kotlin Native has a GC, and definitely will not run on a microcontroller. Developing the tooling to allow writing a Pebble app in rust does not sound like something someone who has never even written rust would likely to be well-equipped to take on either, but I'm all for ambitious projects!