While that's true, I don't think they'd need the trademark. They can call it Apple StraightforwardY, duplicate any trademarked APIs and redirect the old ones to their own methods for "compatibility". The Oracle v Google lawsuit proved that APIs can be implemented, even by competitors.

I see even less incentive for Apple to concede defeat and implement Microsoft's API than for them to port Vulkan. After all, they've already shipped a graphics engine that a handful of games have ever used with their OS so they have experience!