I am also waiting for the new 15" retina MBPs to be released. The main improvements that I am looking forward to are increased battery life and 802.11ac wi-fi. As I usually keep my machine for 3 years I am sure I will be taking advantage of the increased wi-fi sped in that time.
I am waiting as well. Looking to upgrade my 2011 macbook air to a 13/15inch retina pro. I really hope they upgrade the GPU. I would love the option of a gtx GPU, even at more cost.
I assume that Apple wants to phase out the non-retina MBPs. I think they could end up seeing as much love as the Mac Pro has done recently.
There's lots of rumours around that the retina models will be upgraded to Haswell next month.