The risk with X86S was that people didn't really know what the corner cases were. I'd assume if you start with a fairly vanilla system, all modern x86-64 code,

The risk with X86S was that people didn't really know what the corner cases were. I'd assume if you start with a fairly vanilla system, all modern x86-64 code, then yeah it's going to work fine. But I could imagine some of the modes and instructions that might get yeeted could cause unforeseen consequences on more "delicate" software. Obviously this means stuff like "386-only binary applications from 1991" but I'd wonder if some of the weird modes are intentionally triggered by things like copy-protection software to make them less easily reverse-engineered.