Ah yes within the browser space the various companies are just putting web assembly in/alongside the existing javascript engines. WAVM was just an example of a whole new vm that isn't for a browser, but does run webassembly.
Yeah; I probably should've been more explicit in my original comment: there's definitely new VMs being written for WASM, but none are currently expecting to go into browsers, hence concerns about sandbox escapes from browsers aren't affected by them.
It's probably safest to assume that history will more or less repeat itself with web assembly.