Amazing would be if the armor models could be rendered in the same way.

Gonna put this back to On Hold. I don't think this is worth the effort to implement. The armor in mc is nearly fully flat with barely any edges that would use this feature, and most places would be incorrect(like on the arms/boots).

I should specifize what i mean. I relized i asked very vague. The whole armor dont need to be volmetric. Just the helmet should be volumetric. There is a part which is prefect for. I leave you an example here:

If the red squared area would be volumetric, it would work with all armor texture. Even with modded.

Is that part used for vanilla armor? I know that they can technically have stuff there, but does vanilla do that anywhere?

Kinda. By using resourcepacks to replace the vanilla armor yes. The vanilla armor itself dont use. (most resourcepacks and armor mods use it)

I second this! the perfectly thin armor has always bothered me.