The linked paper contains a quote and a reference to Microsoft Singularity that really is an interesting thought experiment. Imagine we were all running next-gen systems designed like Singularity by now, which relies on type safety and managed code instead of memory protection to provide application level security. Spectre would have been a lot more devastating then, if we couldn't have hardware-assisted virtual memory protection separating processes from each other?
https://en.wikipedia.org/wiki/Singularity_(operating_system)