It becoming a stale standard is maybe the biggest threat, yes. It has the issue all standards have since several actors have to play along, except this time it isn't Nvidia, Apple, and AMD, but Wgpu/Mozilla and Google. Their incentives are hopefully better aligned with users than those of the hardware vendors.

I suspect WebGL was different, since it was based on the old OpenGL/DX9 way of doing things, so a clean break was desireable. But I honestly am not that knowledgeable in neither graphics programming nor WebGL history, so take that with several grains of salt.