I wouldn't mind an event specifically for new Macs, or even just silent updates, but I really hope it's going to be sooner than September/October. Intel already released the new chips and a lot of manufacturers already made the switch. Does Apple gain anything by waiting before putting up to date components in its Macs?
It does if Apple is reworking any of the MacBook Pros innards, addressing the keyboard issues or is still waiting on discrete AMD Vega mobile GPUs - then prudence would say to wait on any announcement.
Intel's new Coffee Lake 45w H-Series (six-core versions) CPUs were just introduced on April 3rd of this year. The 5w Y-series (MacBook) has yet to be announced and above all, Intel staggered the roll out of its Coffee Lake (8th Gen, if you will) over a period of 9 months, which is a long time in the microprocessor world. Without announcing the 8th Gen Y-Series, they are, technically, still not done with the roll out.
There is no doubt in my mind that Apple would use Intel's introduction of their 4-core U-Series and 6-core H-Series to their advantage to rework the MacBook Pro making it slightly thicker to accommodate better cooling, a larger tiered battery, a better shielded keyboard with a revised butterfly- or even a modified scissors-based mechanism and turn the trials and tribulations of the 2016/2017 MacBook Pros into a marketing triumph. I can hear almost hear Schiller now, "In order to make the new MacBook Pro the ultimate, no compromise notebook computer, we went back to our groundbreaking 2016 MacBook Pro and re-examined everything!"
This might also be the opportunity for Apple to release a NON-touchBar version of the 15" MacBook Pro, by using the Intel G-Series CPUs (4-core i7 w/ Vega Graphics built-in) and further segment the market, which is what we have seen Apple do with both the iPhone (SE, 6s, 7, 8 and X) and the iPad (mini, iPad, iPad Pro). Doing this would allow Apple to address criticisms of the current-generation 13" and 15" MacBook Pros and turn it into a marketing win for themselves.
And if Apple does have a larger 13" MacBook waiting in the wings, then they are going to want to hold an event to showcase this new computer along with the revised MacBook Pros.
I would not be surprised if the iMacs get 8th Gen CPU updates on Monday, if nothing else.
One last thing, Apple has two optimal timeframes for releasing hardware updates, three if you count March. These are May, June, July (the Back To School season) and September, October, November (the Holiday Shopping Season).