I'm guessing by the thinner case dimensions on the 730 13"/15" that the 8th gen i7 GPUs are the 8850u.   This would be a welcome change from the 6700hq as performance is similar  without the power draw.  I hope they don't cut down the battery in the 15 but likely will. 

I wish the 15" had dual thunderbolt 3 ports like the 13" does.  I know they went with the Lenovo power port because of the gtx 1050 gpu option which is beyond the power deliverable over usb-c.   But its annoying that the 13" has a better port selection in that regard.

It would be nice for example to have a 15" yoga 730 speced like the 13" with dual thunderbolt ports.   Then you could hook one to an dock for ports/power/external monitors and the other to a egpu box when your at the desk.  The 15" has a bigger (which to me as better) screen but its less useful othewise.