So I'll preface this by saying yes! I'd love to have something like that on the site. There's also things like Swift Fiddle (https://swiftfiddle.com) which is plain Swift rather than WASM.
Long term I think running local code through WASM would be great but it's probably outside of the remit of the work group. It's likely something for the language workgroup or the embedded group to actually solve. As workgroup we'd probably be very keen to take something like that once solved however