Almost certainly, Samyang are just continuing to use the EF protocol (reverse-engineered) and have simply changed the dimensions of the mount.Sometime ago, I saw a post by a Canon Japan rep that stated competitive lens Mfgs are exactly that, competitors and to my knowledge, Canon has never shared their tech data with 3rd party lens Mfgs., which leaves reverse engineering their only alternative. . Competitors are not making knock offs or illegal copies. They're just trying to make EF and RF compatible lenses. I don't see the legal restrictions or patents being the problem here. If they were, you wouldn't see Samyang/Rokinon producing RF mount lenses, already. I feel sure that Canon hasn't shared any RF tech data with them.
There is of course no reason why Tamron, Sigma and others can’t do the same. My guess is that they are delaying release of such lenses for 3 reasons:
- they want to design new lenses to take advantage of the shorter flange distance.
- they can barely keep up with demand for their existing lenses.
- Supply chain issues (chips etc)