If it doesn’t really catch on and just ends up being mostly (ab)used for nefarious purposes, I can imagine the major browsers dropping support in a few years. They did with technologies like Flash and Java applets before, and those had had much wider adoption previously.
On the other hand, if someone comes up with a good programming language for modern Web-style applications that compiles down to Wasm for the client side and the ecosystem around it reaches escape velocity, that looks like an opportunity to disrupt a trillion dollar industry to me.
Such things used to seem unrealistic, but there is so much money in web development, the current state of the art is so bad in numerous ways and almost everything is currently so short-lived (by wider programming industry standards) that I don’t think it’s completely out of the question to move the goalposts to an entirely different playing field any more.