I don't think GPU hardware is particularly suited to efficiently emulate those console parts that limit emulation performance today; Vulkan won't change that (although emulators like Dolphin might see a small benefit, also keeping in mind that Vulkan is not only about performance, but more generally about streamlining and a new chance to make more compliant/predictable drivers (Dolphin specifically had/has a lot of problems with rendering bugs on faulty drivers)). Although if it ever is discovered that important parts of emulation of the consoles in question are amenable to efficient computation on graphics hardware, Vulkan might make a difference.
Given that BH has support for old-ish systems up to PSX era at this time, any performance improvement would probably be negligible, and an implementation of a Vulkan renderer more of an experiment (maybe it'd make the rendering-specific bits in BH "cleaner", don't know).
Can't comment on your SuperFX question.
All syllogisms have three parts, therefore this is not a syllogism.
