[ivars]

This is more of a humor (obviously), but

* Blockchain - this is usually the first that comes to mind.

* Rust - "hmm, where would I use it now?" is the question you'll ask if you just learned Rust but knew C++ already.

* Vulkan / Direct3d12 - yes, you now have the ability to recreate your own driver from scratch, but who has time for that? Even Microsoft Flight Simulator uses Direct3d 11. GPU ray-tracing will force you to use one of those though anyway.

* WebAssembly - at least in it's current state.