Modular smartwatches might become a thing in the future. BLOCKS, a modular smartwatch, is hitting Kickstarter on October 13. You can customize this watch with different modules. For instance, you can add GPS, heart rate, altitude, extra battery, and other modules to improve your watch. A wide variety of modules are expected to be made available for BLOCKS.
BLOCKS will have an open platform, so developers and companies will be able to create modules for it. More information about the watch is available here.