Is there any talk about integrating OpenGL tessellation in Unity 5?
Not unless they upgrade to OpenGL 4.0, which AFAIK isn’t happening. Also I’m not a forum cop, but you could of asked about Unity tessellation performance and OpenGL in a single thread :)… Although I care more for logic than forums.
As for performance attributes, subdivision at any level with primitives is going to affect performance levels. It all depends on what you’re using it for?
Our main characters are 1.3Million triangles at sculpt level, we retopo and clean up in Modo and Topogun. Our final product hangs around 15,000 triangles and there is little performance impact.
Off the top of my head the Ocean alone in CryEngine is 526,000 poly’s with tessellation. Still get’s 200+ FPS… So I wouldn’t worry about it too much 
