All the current plug-ins are export plug-ins. I don't believe it is possible to write a plug-in which will do anything else right now (e.g. integrate 3rd party actions like sharpening or noise reduction). I'd love to see this as well -- for example the way to run Noise Ninja from within Aperture.
No idea as to any of Apple's plans for upcoming product versions -- generally they are not very forthcoming with product roadmaps.