Can't really give out any non-public info unfortunately.
I'm not saying that everything was fixed in stone by 8/2021, but any big hardware features like the front-facing display would take longer than that to develop start-to-finish, so I'm just refuting the possibility that Apple could have started development of a front-facing display on the headset and had it ready on the final product in <2 years.
It's not necessarily that a display itself (or any other individual component really) takes >2 years to develop, but that a tightly integrated cutting-edge system can't have significant hardware features added on <2 years before the final product is demoed to the public.