Surely that is a noble goal!

But isn't it a case of XKCD 927? https://xkcd.com/927/

I.e. I would say the probability is zero that because WASM exists other existing complexity of browsers will be removed.

Because the web is so vast, if you once add a feature to browsers you can never remove it because that would break an unknown amount of websites, or even intranet sites.

So now we have wasm + N other subsystems, so N+1, and the security of N+1 systems is less than that of N.