Broadway would only be "incremental" for people who bought Haswell. There are many who own MBPs from 2011 and even 2012 for whom Broadwell would be a significant upgrade because of the hardware changes (faster SSD, advanced Wi-fi, longer battery life, Force-touch trackpad, etc.)
And lets not forget, October's re-design (if true) would be the FIRST version of a brand-new model. Anyone with long familiarity with Apple products knows the perils of purchasing such. The first MBP (I bought one) fairly sucked: overheating issues, old and slow DVD drive, underpowered Core Duo processor). The first Retina MBP (I bought one) had image retention issues and underpowered HD4000 graphics. The same goes for the first iPad, iPhone, iPod touch -- the second versions of each were dramatically improved.
The smart move would be to buy the Broadwell MBP (on Wednesday?), then you can sell for a good price when Apple releases Skylake MBP version 2 (probably in June 2016).
Plus, you fall into the loop where "why buy Skylake, next year's processors will be a HUGE improvement!"
Unless it's like a week before a major Apple keynote, you should just buy as you need.