Figma (https://www.figma.com/) is a design tool that runs in the browser and makes heavy use of WASM. It's definitely slower than using a native app like Sketch, but not slow enough to be completely impractical. A few design people I work with here in India have switched to Figma from Sketch, and they seem very pleased with the results.

I can see WASM becoming useful for enabling apps that do real-time audio/video/image processing in the browser. Games are another obvious use case.

Maybe one day I'll be able to run an Ableton-lite right in the browser.