What would bring PyOpenGL into BGE? A tessellation shader?

PyOpenGL: PyOpenGL is the most common cross platform Python binding to OpenGL and related APIs.

PyOpenGL is an abstraction layer between a (Python) application and the graphics library [OpenGL].

The BGE has an OpenGL binding already.

Tessalation Shader
According to Wikipedia a tesselation shader is part of the graphics pipeline.
This means it is a very low abstraction level (between hardware and graphics library [OpenGL]).

Abstraction layers
In general you can see the abstraction layers like this:
Application -> PyOpenGL -> OpenGL -> OS display drivers -> Graphics pipeline -> GPU

with the BGE you get it this way:
Game application -> BGE -> OpenGL -> OS display drivers -> Graphics pipeline -> GPU

(no claim of completeness/correctness)

As the BGE uses Python you could use PyOpenGL too. But this would be in conflict with the build-in OpenGL binding.

Using PyOpenGL in the BGE can be very nice when combined with pre and post draw callbacks. It allows you to draw things into the scenes like particles using the post draw, or setup an offscreen render target to capture the render output (which in turn allows you to control the post processing yourself). Essentially, including PyOpenGL with the BGE would be for advanced users.

It would probably be difficult to use a tesselation without completely doing the rendering yourself. However, this could be useful if you want to draw terrain yourself.

I see, thanks for the explanation, both.