At this point is seems optimistic to think that there can be a NiMH AA battery that has a capacity of 3000mAh.
I have a lot of NiMH batteries and the best ones I own (Sanyo 2700) perform close to 2600mAh when discharged at 500mA/h.
They hold a charge for a couple of months (at least still after 10 cycles) so I guess it's possible to make them perform a little better (higher capacity but worse self discharge).
My guess is that 2800mAh to 2850mAh now can be accomplished if they wanted to, just after charging and topping off. On the other hand, those cells will probably lose 10-15% of their charge the first day.
I'm very happy with my Sanyo 2700 cells, after testing it seems they hold a charge for months as well.