Webassembly is now a supported platform for CPython, and can be used via e.g. the Pyodide project to produce in-browser tools. I'd love to get Z3-backed testing working in this demo of hypothesis-crosshair, for example.

Since Z3 already has wasm builds for js, and many Python libraries with native extensions already support wasm (e.g.), I'm confident that this is practical - if also a bit fiddly to set up.