Here's the issue with the MacBook IMO: it doesn't really fit an actual category bracket with specs and price. I don't even have an issue with the single USB port, and here's why:
This machine looks like, from the specs, the ultimate budget user notebook. It's small, light, has Retina(!), and completely silent. Plus it'll come with 8GB RAM standard (enough for budget users), and 256GB SSD storage. The people this will appeal to (and I believe the focus) is the girl (or boy) who wants something trendy that's not complicated. And the fact that it doesn't have a power brick will appeal to many.
But it is not for the power user. For most people this would appeal to, I could see the adapters not being an issue. People will get the $79 adapter and be done, they can connect the flash drive (which they probably won't use that much), an HDMI display, and still charge the thing. For anyone with any real computing needs, you'll still need the Air, which will still be a faster machine that the MacBook, or the Pro.
And herein lies the issue: it's got budget specs, everything is in its favor to appeal to the mass-market Internet user, and it's $1299!!! That's the same as the Pro Retina 13"!! The price is the problem I see here, because it is basically spec'ed lower than the Air and it costs more than the Air, so the only thing that will actually draw anyone to it is the Retina display. The Air has an advantage in just about every other way, not to mention that you could get a Pro for that price. If the price were much lower, I think it would be a better product.
Making a budget product with a pro price may very well be a big problem for Apple. I like the concept of the product, but the price will turn many away IMO.