I'm not sure whether many different implementations is inherently good, though.
Firefox has not enabled WebGPU via wgpu for the same reasons Chrome Security has done an in-depth review of Dawn. It is a component that must be hardened. For anyone out there trying it out by enabling config flags, remember to disable it once you are done. It will be ready in time.
Until you run multiplayer and are suddenly dealing with hostile players, servers and possible mods.
> SV_SteamAuthClient in various Activision Infinity Ward Call of Duty games before 2015-08-11 is missing a size check when reading authBlob data into a buffer, which allows one to execute code on the remote target machine when sending a steam authentication request. This affects Call of Duty: Modern Warfare 2, Call of Duty: Modern Warfare 3, Call of Duty: Ghosts, Call of Duty: Advanced Warfare, Call of Duty: Black Ops 1, and Call of Duty: Black Ops 2.
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-2081...
I am not attempting to claim that games do not have security issues or cannot experience remote code execution, just that this is not a normal pattern of behaviour that they plan for, so it is normal that a game author would deploy wgpu long before Firefox does (while Firefox spends a lot of effort on fuzzing, etc). If anything a terrible CVE that Activision has expended apparently zero resources fixing is a very good example of what I'm talking about.
Depending on the game, it downloads maps, skins, etc. from the server... File parsing code is highly suspectible to security bugs.
Aside from that, the Bevy game engine also uses wgpu on non-web, but afaik no game of particular significance or player base has shipped with it yet. I think the biggest user of it is actually a software tool for mining (the hardhat kind), but it's a "call us for a quote" kind of thing so hard to tell how big it is.
Additionally wgpu and WebGPU aren't the same thing, as wgpu exposes native features as well.
Those examples you gave are not comparable at all, ativex and flash are way, way higher level, don't operate at all like graphics API middleware. PNaCL was a WASM alternative design, which thankfully lost as WASM is much more flexible.
My point is that WebGPU is way better positioned than any middleware, it has industry backing and official support from all relevant platforms (or plans for it). It's also benefitted a huge amount from hindsight.