I’m a proponent of having a C++ API. The RNA API that is used by Cycles is work towards that. However it’s a big project to make that good and stable enough for public use. At the time of Blender 2.5 I was hoping someone would pick up that project, but it didn’t happen and we didn’t have time ourselves.
I welcome development in this area, but the developer working on it needs to be prepared to do some big refactoring and deep changes to Blender. Probably for it to be really useful, first we need to do the kind of refactoring that Stefan refers to. The best entry point here is if we have a node system where you can implement a node in a single c++ file, which we are thinking of for the new function nodes design.