Plans to support OpenGL 4.3?

You're right -- Parallels currently supports OpenGL up to 4.1 (per the KB article you linked). From what I've seen, the limitation is tied to Apple's graphics stack on macOS, which restricts Parallels' ability to go beyond 4.1. VMware Fusion works a bit differently because of how it translates graphics calls, which is why you might see support for newer versions there.

That said, Parallels has been gradually improving graphics support (for example, adding DirectX 11 a while back), so I'd expect OpenGL updates to come eventually if there's enough demand. Unfortunately, there hasn't been an official timeline shared for OpenGL 4.3 support.

If your workflow requires 4.3 specifically, you might want to keep an eye on Parallels' release notes or submit a feature request directly to their support team -- they do take user demand into account.