I believe I have a need similar to the OP's.
I don't see why you'd need such an API. It's only useful for native contexts, it has nothing to do with FBOs. Also, these functions return native handles, which will have to be wrapped by LWJGL somehow. Something like that will have to happen in 3.0 anyway (we'll probably expose more low-level stuff than we do now), but until then I don't see any significant benefit to exposing such functionality.
I have a GL context created by another application and would like to render on it in a Java application using LWJGL. The only thing preventing me is that there seems no way to use that context in LWJGL - I can only create a new one (by creating a Display, for instance).
I believe I see the problem - in order to wrap LWJGL around a native context, it would have to know about its capabilities to map the functions correctly. I could personally imagine something like
GLContext.useCurrent(ContextAttribs) being enough to provide an unchecked and inherently unsafe wrapper around a native context - but that unsafety should be the responsibility of the developer who does shady things like this. It can be really useful.
Though, I might miss something here, I do not know too much about LWJGL's internals. But if something like this is due to be added in 3.0, I'm all for it.
