Never. They will never release them. Muhahahaha.
But seriously... never. By the time they do, sandy bridge will be released on a whole new platform. And Intel has managed to keep on top with their overpriced quad cores. Now that the i7 980X is $1000, if they were to release anything else lower, they would have to bump down the prices of their quad cores. And why do that if business is booming and Sandy Bridge CPUs are being released on a new platform next year?
Let's see if my prediction comes true and they never release affordable 6-cores on the 1366 platform. If so, I would hazard a guess at affordable 6-cores being released in 2012. Unless bulldozer from AMD provides enough competition forcing intel to release better CPUs at lower prices.
If you aren't happy with your Core 2 quad's performance, I think you might have to wait a lot longer. Or look into a server platform if you really can use all the CPU cores. You can get lower clocked quad cores from both AMD and Intel. Get two of them and put them in a server motherboard with two sockets. 8 cores. AMD also has 12 core CPUs. So if your programs really are efficient at multi-threading, you can sacrifice individual core performance and get a 24-core system. Those CPUs are more expensive though. Although, not as expensive as the 980X.
If you really aren't happy with your current performance, I'd start saving now, wait a year for AMD Zambezi and Intel's Sandy Bridge and see how the performance is. I think Sandy bridge are improved versions of the current i7 processors on 32nm. From what I gather, Zambezi will have up to 8-cores and improve greatly on ALU performance. Something about modules and each module appearing as two cores but having two ALU units and one FPU unit.