From the AnandTech review, 3D particle test was showing AVX512 effect nicely:
https://images.anandtech.com/graphs/graph15044/113590.png
10980XE had 3.9x speedup compared to 3970WX per core using AVX512.
So for some scientific computing purposes (maybe game physics?) AVX512 is worth it.
Not game physics, as it puts the CPU in a lower speed regime it'd have negative implications on the rest of the games performance. So far, that AVX512 requires this lower speed (due to thermals) is an implementation detail, and it could be expected that newer processes (Intels 10 or 7 nm?) would allow them to work AVX512 tasks on full speed.
Until that happens, and everyone has AVX512 (because it'd be a massive fail to have a game that requires you to have a HEDT Intel processor to play), it'd be a nice gimmick to have on very specific tech demos, and performance sensitive scientific code that you know will run on a certain machine with certain characteristics.
Game programmers will put time into making slow CPUs faster. Outside tech demos or hardware marketing tie-ins no budget is allocated to making yet more spare capacity.
That said, desktops can apply whatever optimizations they want. Denuvo uses AVX in their DRM, which is also not a thing on console, so presumably they will eventually incorporate AVX-512.
There are also various libraries that leverage metaprogramming to do similar things. I don't think you understand what game devs are willing to do, to get a few more polygons and pixels on the screen!
Totally depends on the trade-offs. You can write your whole game in assembly, and target very specific hardware, and may be beat optimizing compiler (doubtful). But at what cost? Time spent on that could be spent on making more games.
Normal up to date hardware handles games just fine, as long as they are not using some abysmal and poorly parallelized engines. Modern CPUs with more cores are also helping that, especially after Ryzen processors opened the gates for it.
AVX-512 isn't just wider execution units, it's different types of instructions, particularly some that fill in holes in the existing sets of instructions. Once it starts to be widely available, it will get used, and will eventually be a requirement, just like AVX has.
Ice Lake is introducing AVX-512 on Intel mobile, Tiger Lake will introduce it on desktop, presumably Zen3 will be introducing it on AMD.
its also relatively common to write multiple versions of SIMD code (or use tools like ISPC or metaprogramming) to leverage whatever SIMD instruction set a cpu has. Such as the DOTS system in Unity. Games will happily leverage AVX-512 as soon as a fair number of desktop cpus support it.