You will see it explode indeed (where "it" means "the browser" and "explode" means "tab gets throttled and/or crashes"). I understand the motivations for everything-in-a-browser, but this approach has major externalities - e.g. the client's power, both as in CPU and as in battery.
Something like a torrent network is a bunch of IO with some processing which fits perfectly with javascript. WebAssembly might be able to get around some of the performance issues in specific areas (like some of the more complicated hashing stuff) if there are some, but it's more than possible to write performant code in javsacript.
It might be possible, but I have yet to see it. So far, the performance increase has been thanks to the engine executing such code, despite the opposite effort ;) of the JS code.
