I actually like BK's idea of a dreadnought-style unit.
We have tomb-spyders, but they don't really cut it at shooting. Fluff-wise it would seem plausible that the spirits of some the necrontyr were splapped into a larger chassis than the standard necron warrior or immortal bodies. A must in any future units would be different weapon options, so having a choice of either gauss cannon, gauss blaster, or a cc weapon of some type would be cool.
The alternative would be to have its weapons function in a similar manner to Chaos Obliterators, changing between the different gauss weapons or a combination of them as needed.
I've also thought that the Necrons needed some more 'classical' robotic units. I don't mean a little R2D2 with a gauss rifle, but perhaps a small tomb spyder (with a high BS but otherwise lower stat profile) that could fly around taking pot shots with gaus rifles.
GW should pay me for my brilliance.
Pauk777