Hi Phil,

It might be tommorow or it might be next year.
There is talk of a D600 FX body.
The D300s is getting very old too, though some speculate there won't be a D400. We won't know until Nikon makes the official introduction.
If you have any AF-D screwdriver type lenses you might want to consider the D90 or D7000, since both have AF motors built into the camera body. They also have Commander mode built in. The D5100 does not.
Good Luck and Enjoy your Nikons!

Best Regards,
Marty