The issue is that; if the rMBP is released tomorrow, there probably won't much much of a graphics upgrade over the current one; at least for the 13" type.
They basically have three choices:
- use the available 28 W SKUs (or possibly the quad 37W 4702MQ), which would be the logical choice for the 13" pro. But this would leave them with HD 4600 graphics, which is only a small upgrade over current offerings.
- use the available ULV offerings, and get that 40 EU part for graphics (HD 5000 series) without the eDRAM; but the CPU performance would be drastically curtailed compared even to the curr generation.
- Wait for the 28/37W SKUs that have mainstream M series performance (base clock 2.2GHz +), and also have some form of GT3/GT3e graphics (Iris, Iris pro) that would be a big leap from curr gen graphics. But this won't be released until late october timeframe (give or take a few weeks).
The 15" really doesn't really matter that much in terms of what iGPU is on-die with intel SKU, since it likely had a discrete solution built-in anyway. Unless they are thinking about offering a 15" with integrated graphics again, like they did 3-4 years ago.