I also really hope they will be playable at some point. And I strongly disagree with people saying they are NPC material. The latest Codex reinforced the notion that all the more powerful Necrons are sentient individuals. Which is completely unlike the Tyranids which are controlled by a Hive-Mind and thus prime candidates for being NPCs.
Nercons as an NPC? are you jokeing? There are fit for players. Just as Cronty route up there are sentient individuals that have a personallity and renember everything before there race was changet in too an android body's. So basiacly an NPC could be basic Necron Warrior, but Nercon players will be a specialist of a diffrent class then an ordinary warrior, Necron Lord for example, the Cryptyk, Tomb Guardian etc. It can be playable
I smell highly overpowered chars on the way But yeah you are right the more specialized and high ranking necrons would fit to player characters. I personaly see a balance issue on this but then again it's not something the devs can't fix. So as long the dev stays in the fluff I'm ok with necrons but I see the bulk of necron forces (warriors, spyders, scarabs etc.) as NPC chars more than player chars. Sorry
Necrons are awesome and there is little reason to not have them playable. They are soulless, but not mindless.
They are not souless, the newest Necron Codex rights othervise, ther reagain there souls when the destroyed the C'tan and bend them to the Necron Lords will.