Epic, Crytek, DE, Croteam, DICE,... doesn't rewrite their engine with every iteration. It's the same code
FSR is done. The game already included an upsacler and they just added CAS to compensate for the blurring of the upscale process. But I don't really see how this would improve the quality of the graphics (like DLSS). It's more solutions to allow companies to invest less in optimizations.
Vulkan and Dx12 are not supported by the Xbox 360 and PS4, which would require support for several APIs within the engine. How to say...