In fairness they have been repeatedly nerfed into the dust over the past several years. The only thing is that it has been on the tabletop rather than in terms of lore.
Back on topic Have you ever thought of having the old ones as a faction? Back off topic You never know who could be watching *cough, GW, cough*
The Old Ones probably run around in another dimension for they are masters of dimension. I rather would not like Dimension-Wanderers as a faction. They just would phase out on a shot and come out behind you and do go figure what. Or probably they have dimension-phaser guns which teleport you go figure where.
No, they are not a mix of Necrons and Eldar.... More like Eldar, Human, Ork Mix +5 on all attributes. They have made the Humans, Eldar and Orks and probably many many many other races too. Wouldn't be surprised if the Tau are their work too.
ork and dark elder, feel like there isn't enough :u (kinda worried about what a necron supplement would look like...(see "Matt Ward"))