> You'll then have to convince Microsoft, Apple, Google, IBM RedHat, Canonical, the Debian project, and a few others, to actually package this VM with their OSs, so that users don't have to manually choose to install it.

I think this is the easy part. Everyone is already on board with webassembly. The hard part would be coming up with a common api which paves over all the platform idiosyncrasies in a way that feels good and native everywhere, and that developers actually want to use.