Hello,
I don't quite understand the need. OpenGL is an open standard and can be used in multiple systems, including windows. Why not use OpenGL directly?
There are various reasons to use Direct3D, most having to do with trasportability of some sort. In particular if one wants to move code to an Xbox(360).
That's it. What I want is to be able to deliver graphics libraries that don't speak to a specific type of users (namely OpenGL users, even though I'm part of them). Moreover, this kind of library could serve as an extensible framework to "easily" implement support for over implementations. For example I'm currently doing quite the same kind of work to enable a little engine I've written for PSP and then ported to PC, to run on both with the same code.
But 3D graphics is a mine field when it comes to what abstractions, features, and implementations to support. It brings up even worst nightmares than the GUI discussions have brought. I suggest Boost stay clear of such a library at the moment, it's just not worth the pain.
You're probably right and anyway, the need for spatial data structures is much more important than this need (it can even be a precondition to it). Bruno