Are the Devs aware of the unlocked core for PS4? And will they use it?

[Colorful]

The PS4's CPU really isn't a limiting factor of FFXIV's UI, it's the amount of ram available on the PS3. As for connecting to the PS4's OS, I have no idea what you mean as I haven't seen a game do that other than the already integrated features. What you could expect is more stable performance, but barely so. The PS4 struggles to maintain a high FPS in crowded zones or 24 man raids, they're not about to make it struggle more.

Probably. I guess thats part of releasing the DX11 version soon for PS4.

It's been said many times, but the PS4 doesn't utilize DX11 nor could it as it's a Microsoft "product". The PS4 has its own low-level API which is more efficient than DX11.