Yosemite AFAIK is still OpenGL 4.1, if they were going to update it then I’d have expected them to announce it at WWDC.
To be clear - OS X’s OpenGL 4.1 supports Tessellation. However, UE4 only supports as part of its Shader Model 5 rendering path, which also requires compute shaders and a few other bits & pieces. Since decoupling this is pretty tricky and isn’t regarded as a super important feature to expose on OS X right at the moment, UE4 on Mac doesn’t compile or run any of the shaders. World displacement is dependent on in order to work, so it naturally follows that this is stuck waiting for support to arrive. In essence, it is not a high priority to get support working on the Mac, so it won’t arrive anytime soon. It will be supported eventually, but much, much later.
There are no plans that I am aware of to reimplement Reflections on Translucent Materials for Shader Model 4, but that work would fall outside my domain, so I could be wrong.
In both cases as soon as Mac OS X gets the underlying technologies for Shader Model 5 these features will be supported, but probably not until then. If you want them adding to the roadmap, then perhaps make your case on this thread: UE4 Roadmap - Feedback & Requests - Epic Developer Community Forums