I'm very excited about a Retina display on an iMac, whether it comes out on Oct 16 or a year from now. Like many folks here, I do a ton of photo and video work, and a 4K or 5K display would be a dream to work on. I could very much use a Mac Pro, but when you take a look at the prices, you get so much more price-wise with the high-end iMacs. I just can't justify the price for a Mac Pro.
If a Retina iMac is released on Oct 16th, I'll wait and see real-world results from whatever GPU they use to drive it, and if need be, I'll reluctantly wait another year if stronger processors are needed for an optimum experience. I guess we'll find out soon! Good times for sure...
Bryan