"It's the right move, but is it truly better than ITX or uBTX?"
It is sized to maximize use of a panel. That is a big plus. It is backwardly compatible, so it fits in the cases that are out there. And it isn't overspecified, as the article notes that uBTX is. Giving the manufacturers a bit more freedom. So the fact that this prototype doesn't have a PCIe slot means little. As the single pair of DIMMs, although 2 pairs might be tricky to fit in.
This is the perfect standard for the commercial market.