retroarch supports it as a graphics driver but it's used for simple blitting to the screen, so no perceivable advantage in 2d emulators. another side effect is that the usual GLSL shaders we use will not work with vulkan - you have to use SLANG ones.
3d cores and standalone emulators may have vulkan implementations, which would take advantage of the new speed/features. lr-parallel would be a fun experiment (though i expect not viable at all). duckstation, beetle-psx, flycast, ppsspp, and dolphin are potentially viable ones that i can think of.
another issue is, does the vulkan driver still need X? that's not ideal.
Most of the links go over similar steps for compiling, installing, and testing Vulkan and its demos. Some additional notes:
The older posts point to a developer's fork of Mesa. Now that Vulkan has been merged into Mesa, whereever you see a git clone you'll want to make sure that you're pointing to Mesa's repository (https://gitlab.freedesktop.org/mesa/mesa/)
You'll be able to get Vulkan from the master branch of of the Mesa repository. It doesn't look like it's been tagged to a release yet, so there's likely more work to be done and your mileage may vary.
You can actually have different versions of Mesa installed on your system simultaneously, as long as you put them in different directories. In order to ensure stability of my Pi systems, I do this, so I can test and play around while not worrying about everything else. Though Mesa is pretty self contained so it's not too hard to get things back to normal if you overwrite the original drivers.
If you have compiled Mesa for installation in another directory, then you'll need to add the following line to your launch scripts or your bash profile in order to point programs to your special installation. You do that with the following line:
export VK_ICD_FILENAMES=[YOUR INSTALLATION PATH]/share/vulkan/icd.d/broadcom_icd.armv7l.json
I've found that Raspbian/Raspberry Pi OS (which is what RetroPie is built on) actually uses NVIDIA's Vendor Neutral Dispatch version of Mesa (which uses code from Mesa), and not Mesa's version of Mesa. I have no idea if that will be changing or not, but it at least indicates that there will be more work to do before we see Vulkan drivers as part of Raspbian/Raspberry Pi OS/RetroPie as a default.
I've been playing around with Vulkan and so far it's looking pretty good. I have high hopes that as programs begin to adopt Vulkan we'll be seeing some really awesome performance increases. I have not tried Dolphin though. The only thing I've found regarding Dolphin and Vulkan was someone testing it out on a Jetson Nano, which is a different hardware platform. He did compare Vulkan vs. OpenGL and found that Zelda: Wind Walker ran very well with Vulkan where it was choppy on OpenGL. The post is on Facebook (https://www.facebook.com/groups/retropieofficial/permalink/1387063751494192/).
I created a scriptmodule for my own purposes to automate building / installation of Mesa with Vulkan. I may create a separate post for that.
a self compiled version of ppsspp with vulkan support. conclusion: vulkan works, but framerate on vulkan lower than with opengl backend
a self compiled version ofr retroarch with lr-mupen64plus-next with vulcan support. On the normal open gl renderer it works, but gives a segmentation fault on the angrylion vulkan rendererer
a self compiled version of retroarch with lr-parallel: same segmentation fault on the same renderer
so apparently a lot of work to be done before we get benefits using vulkan....