I think WASM will have a great future in the cloud, giving cloud providers can offer their services in any programming language their users want, running in a secure sandbox.

But i'm not so sure about personal devices. It would be very hard to beat Javascript code on the Web in general. So i dont know about the general purpose target future in that case, i think it will flop, except as a fancy accelerator or to virtualize things that was once outside the web.