Earlier quoted context omitted.
The game engine segment is much like the operating system segment - the size, momentum/inertia of the incumbents (ie. UE4, Unity as an analog to Linux, Windows etc) make it rather difficult for new entrants, especially for ones written in languages that are not as popular as C or C++ (eg. Rust). It's simply too hard right now to find enough programmers proficient in Rust who could assemble a competing product, IMHO.
I'm excited to see what happens with Embark Studios; EA SEED started using Rust for stuff, and Embark is a new studio founded by some ex-DICE/SEED folks that's doing everything in Rust. There's also Ready at Dawn and Chucklefish...
Don't get me wrong, I'm optimistic, and I'd like to see it happen. Although I was a C/C++ holdout at first, I'm starting to come around to the Rust way of thinking, even if I don't like a lot of the terminology and the "RIIR" crowd are completely annoying.