"So, which processor?
The days of Apple getting the first shipments of a new processor are well behind it. We have little faith that Apple will be the first vendor to supply a Kaby Lake desktop repacement laptop. That leaves only Skylake available for a September release, unless CEO Tim Cook has something up his sleeve.
While it is accurate that the first quad-core Skylake processors suitable for a MacBook Pro have only recently started shipping, there were other options before the April release of that particular model. A laptop Xeon processor was available in January, which could have been used, which met all the criteria that "power users" demand from the hardware -- but Apple chose to not use it.
Compounding the problem of a long update period, the forthcoming Kaby Lake S-series has significant features that would be great to have in a refreshed MacBook Pro. Full, native support for Thunderbolt 3, and full speed USB 3.1 Generation 2 are big, but given Apple's inclusion of integrated graphics in the MacBook Pro, the improvements that Kaby Lake will have would be greatly welcomed.
From a benchmark perspective, the 2012 Retina MacBook Pro with a 2.3 GHz i7 processor is only slightly behind the 2.2GHz i7 mid-2015 Retina MacBook Pro. That isn't Apple's fault, though -- Intel's delivered their end of the bargain with new processors, but the new silicon hasn't been that compelling from a sheer speed point of view.
The last few iterations of Intel chips have seen only slight increases in performance, most in battery life. Apple's battery technology and control over the hardware has mitigated the negative marketplace effect of not moving to a newer processor in the interest of long battery life, but that time is soon to be over.
Apple is bleeding Mac users, mostly from the content producing side from lack of updates because of the infrequent updates. The loss and overall market perception of the Mac lines for professionals has gotten so bad, that HP's line of workstations was promoted with a network access function to allow macOS users left in the dust to do "heavy lifting" remotely.
It's well past time for Apple to update. Cook and company can't wait for Kaby Lake if it wants to retain the "pro" user cadre, but it may already be too late."