I'll add a citation from
Anandtech here for that.
General release appears to be end of September so just in time for an October launch. As noted there there is no increase in base clock speeds although the turbo speeds are up 500-700MHz. I wonder if that's not very helpful for Apple though in their quest to design ever smaller enclosures?
If they go with the older Kaby Lake Refresh i5-8250U (with a handsome discount) in the next few weeks rather than wait all the way into October for these CPUs that may not turbo to the higher limit for long in a power efficient way. Those people hoping to hammer their computers on a budget may find themselves additionally stymied by throttling in a laptop enclosure.
It's not really a problem for the iMac and Mac Mini in their current cases since they can theoretically dissipate more heat and, crucially, might be able to accept a version with discrete graphics to compensate for the reduced graphics performance over an Iris Graphics part.
Apple have to be looking at acceptable performance for driving a 4k screen for the 2018 iMac 21.5" base SKU and I would imagine they will have concluded that UHD620 to drive 4k is insufficient.
I would infer from this that the Mini might see the usual 3 models based loosely on the 2011 marketing model:
Base: Specced to meet a (low) price point
Middle: The one with built in discrete graphics for convenience - HD as standard but small Fusion/SSD choice.
Top: The best storage options (lots of Fusion Drive and SSD) - add an eGPU of your choice later.
If priced right there might be a LAN gaming audience for the middle model while pro users could take the top model and add their own eGPU.