History has proven the exact opposite, as the failure of Smalltalk and the ascendancy of the web browser demonstrate. And as I assert, Dan Ingals is incorrect.
Last time I looked into it, the Web browser is a OS agnostic platform and JavaScript influence in tooling traces back to Smalltalk via SELF influence.
There are even two Smalltalk like development experiences Web browser based, Amber Smalltalk and Lively Kernel, the latter from Dan Ingals.
The OS should be an implementation detail of language runtimes, as proven by serveless computing and cloud native development, who cares if those runtimes run on top of an OS, bare metal or a type-1 hypervisor.
Anyway a modern OS where this is partially there, is Android.