Battery size and battery time are the primary constraints for a wrist watch. The power efficiency of a SoC that runs full blown Debian, as well as Debian itself

Battery size and battery time are the primary constraints for a wrist watch. The power efficiency of a SoC that runs full blown Debian, as well as Debian itself is much worse than the NRF52 used in PineTime. Without doing calculations, I would estimate 10-100x. With corresponding increase in battery size or decrease in battery time. That said, I believe there are smart watches that run Android on Linux, and they do manage 1 day of use.