These userspace runners seem pretty revolutionary, especially their ability to catch syscalls. As I understand it, this is what WINE is trying to add to Linux (so that they can correctly emulate Windows calls for some DRM/anti-cheat).
This is very, very, cool stuff. It positions Fuschia as approximate to a lingua franca OS.
At the end of the day, x86 is x86. Different operating systems use different loaders/dynamic linkers, different filesystem layouts, different APIs, but still the same machine code and still the same calling conventions. WINE, in a nutshell, merely presents the Windows environment (by wrapping Linux calls in Windows calls) to an executable that is running otherwise natively, there isn't a virtual machine or an emulator involved. There is no sandbox or security (as that is a non-goal).
The problem is that various DRM and anti-cheat products use undocumented Windows syscalls to do their job, and syscalls are something that you can't just wrap with a function. This extension will allow WINE to ask Linux to send it unhandled syscalls (via SIGSYS), so that it can emulate them (making it a misnomer for the first time).
Unfortunately you can no longer create syscalls in NT subsystems (XP was the last time that was possible). I assume you have to be Microsoft, or a specially privileged partner with source access, in order to do that.
This is very, very, cool stuff. It positions Fuschia as approximate to a lingua franca OS.