Personally, I don't think they will make a 7000 version. As for a 6850, I think it is definitely in the realm of possibilities. PCIe isn't taking over very quick, partly due to the lack of PCIe AMD boards. But, ATI is definitely moving away from AGP and I think nVidia will follow suit.
AGP is definitely in the majority of systems and will be for some time to come.
I guess there is always room for the next video card refresh to include AGP versions. So, you're probably right. They may include a 6850 type model in the spring refresh that will most likely be AGP or PCIe with an AGP bridge. As for me, I think the difference between the current large technology jump and the smaller refresh jump (just increasing clock speeds and memory speeds) will have only a small impact. So for me, I would snatch a 6800 when the prices start to come down.
However, if you want the very last AGP card, I think you'll need to wait at least until the next crop of cards comes out. I think that's where the AGP line will officially end, since AMD and Intel will have PCIe capbilities and both ATI and nVidia will have native PCIe solutions. You may even need to wait until the next-gen hardware. I really don't see PCIe taking over from AGP as fast as the tech market would want them to.