I would love this too, I am on a ROG STRIX X99 GAMING motherboard and just picked up a ASUS EKWB 3070. My board has some short coming which has me looking at a x299 upgrade but I am having a hard time deciding on compromises even with that platfrom. Even with the newer platform information still seems less plentiful....
I have a u.2 and m.2 nvme... on my exisitng board I would love not to have to choose one of other like it makes you do now.... I have my u.2 drive currently in my second 16x slot... with my new graphics card PCIe_1_1 is not free but if I enable it I loose my bluetooth/wifi. Stangely I still see odd compromises like these even on some the x299 boards even with 48lanes now