This seems like a kludgy solution and I'm unsure what the problem they think they're solving is. Is it making their NUCs repairable and upgradable? If so, sticking with more standard parts (like a socketed CPU and an STX-sized motherboard with a PCIe slot) would have made more sense. Is it making a SFF solution with room for a dGPU? If so, bolting a whole daughterboard onto your motherboard to handle your PCIe slot seems weird, too. It does succeed at being "modular," in the sense that the CPU, RAM, IO, and some storage are on the same easily swappable board, but I'm sort of unclear what benefit that brings other than being admittedly cool.
Also, one of the big problems with "modular" PCs (and phones) has always been platform commitment, and I don't see this being much different at the end of the day. If Intel doesn't keep making or revising these boards the fact that they're theoretically easily replaceable doesn't make a lick of difference to the end user.