I have been looking at the OpenTK Font system and I wanted to make some comments. I hope I don't come across as too pushy. Please feel free to correct / enlighten me if I am just missing the point.
I am very impressed with OpenTK and I am excited about using it for my project. I wanted to start by talking about why I like OpenTK so much as I think it will help provide color for my Font related comments.
OpenTK is a C# binding to the OpenGL API. It provides me with a way to write OpenGL programs in C# without the need to learn the OpenTK "way" of doing things. I can read the OpenGL specs and implement what I read with very little modification in OpenTK. As I get good at writing programs using OpenTK, I am also getting good at writing OpenGL programs. To me, this is a non-trivial factor. It is my long term goal to know OpenGL. It is not my goal to master any particular wrapper library. OpenTK allows you to "think" in OpenGL. This also benefits me in that OpenTK does not attempt to repackage OpenGL in some OO framework that would end up adding complexity and limitations with (in my opinion) little real benefit to the programmer. Sure, I am already making OO wrappers for some OpenGL objects, but these are easy to make and specialized to my needs. My simple FrameBuffer class built to my needs was trivial to construct and will likely outperform something that attempts to be a general purpose FrameBuffer class that EVERYONE can use. I also like OpenTK because of the enumerations for OpenGL functions parameter. This really simplifies things without any perceptible downside.
OpenTK does not stop at being an OpenGL wrapper. Clearly the binding to the window systems, math libraries, and such go beyond just being an OpenGL wrapper. Again, OpenTK does this in a restrained, tasteful, and more efficient way (IE no FreeGLUT / SDL). The GameWindow class does its job of providing a context on which OpenGL can operate without forcing too much onto the engine design.
So now I come to Fonts...
When I think of text drawing in a 3d environment. I think of a textured mesh on a plane. I think of some extents clipping.
Because of this, I think OpenTK should view text drawing in 2 stages. The first stage should be designed around creating an OpenGL friendly list of textured vertexes. The second stage, as a helper, can be provided as an optional means of rendering those textured vertexes to the screen.
There are many use cases for drawing text that my not be suitable to the second stage, that would still benefit greatly from access to the first. For example, I would imagine it would be awkward to try and do "star wars" style scrolling text in the current system.