Air possibilities: There were four 15W Haswell processors with HD5000 graphics Apple could have used for the new MBA.
Air actual: They chose to offer only these two of them.
13.3" Iris possibilities: There are three 28W Haswell processors with HD5100 "Iris" graphics Apple could use for the next 13.3" rMPB.
15.4" Iris Pro possibilities: There are three 47W Crystal Well processors with HD5200 "Iris Pro" graphics Apple could use for the next 15.4" rMBP.
15.4" non-Iris possibilities: There are four 47W Haswell processors with HD4600 graphics Apple could use for the next 15.4" rMBP, if they for some reason decide to give their top-of-the-line laptops drastically worse everyday graphics performance than even their bottom-of-the-line laptops and require extra space in the chassis for a dGPU thereby shrinking the battery and increasing power consumption to obtain worse computational graphics performance and only marginally better framerates in some games.
Note that of the four 47W chips with HD4600 (what the dGPU crowd clamor for) only one of them has the 37.5mm x 32mm x 1.6mm form factor. The other three are 37.5mm x 37.5mm x 4.7mm, which is kind of a lot bigger (especially a lot thicker) for something that goes in a laptop (and requires a dGPU as well to function adequately.) Meanwhile all the 47W Iris Pro chips are 37.5mm x 32mm x 1.65mm, and one of those chips was already seen in benchmarks.