Take a step back from the "hybrid" thing and look at the mobile computing space. And I suspect one reason why no one is "emulating" the Surface, which really is ground-breaking, is because Microsoft pissed off their hardware manufacturers; to copy design at this juncture is to admit that Microsoft's purpose in prodding manufacturers to take design risks was actually correct.
You know what other computing segment had a majority of 10-11" screen sizes? Subnotebooks and later netbooks. And certainly the former, high-end category was targeting mobile business users. The subnotebook space is now mostly limited to Japan since the netbook era killed it in the West due to pricing, which was subsequently killed by "ultrabooks," but 10-11 is actually a sweet spot. I owned two 10.6" subnotebooks from Japan back in the day, and before that an 8". I have a 12" at work, but it's a sloggy heavy laptop inappropriate for mobility, and is just connected to two 22" monitors. The 8" was definitely too small, and anything larger quickly moved into the "thin and light" category unless you get some really nifty engineering (then we're talking $4000 imports). The 13" ultrabooks are actually, to me, closer to the classic "thin and light" space.
What I've noticed over the past 10-plus years in ultramobile computing is that smaller+functionality is a much harder area in which to succeed due to engineering demands; bigger is simply easier and cheaper.
But this is a tangent.
In terms of the big picture, the real reasons why either Surface hadn't taken off are not pinned to a particular hardware spec like "screen size":
1) Microsoft royally fucked up marketing by targeting the wrong consumers and confusing people as to capabilities and limitations and differences from existing categories. Microsoft made the error of leaving Outlook off RT (which cripples it for most business considerations) but also not heavily marketing the particular usage strengths to students or regular users. Basically, with #1, Microsoft should have picked and really targeted a particular usage sector. Education should have been the first choice, and social media would have picked up the rest. Instead, from what I understand, MS tried the generic marketing approach. Bad. (The first Surface ad I saw was after I already bought my RT, and it involved some idiot guy dancing and snapping the keyboard/kickstand throughout a building with other people. What was the fucking point?)
2) The combination of "low" battery life, additional software licensing issues, and base cost were most likely the real practical reasons why the Pro didn't take off in the business sector, along with the fact that many businesses have already both desktops/laptops and awkwardly shoehorned iPads or whatever into their ecosystems: Business ecosystems take a long time to rotate; my department in a multinational company is only now getting Windows 7 and Office 2010. How long does it take to rotate actual hardware after the initial investment? A long time. There are also contracts involved. It's completely unrealistic to think companies, especially large ones, would automatically jump at any "perfect" solution when they've dumped millions into extant systems, and the Pro specifically wanted to replace both primary and secondary devices in one go. It's still a great idea for a fresh start, but complex adoption is plain hard.
3) So many reviewers didn't know how to review either Surface, by making the critical mistake of comparing the RT to an iPad, or were biased towards Apple/Android/anything else, or didn't actually try to use the thing in everyday terms, or were plain incompetent. I immediately discarded a handful of negative reviews because the writers did not know the difference between memory and storage space. But bad press, incompetent or not, is bad press and can be eternally damaging outside any objective merits.
4) Too much brand loyalty and thus brand hating. Once you add lovers/haters to the brand mix, any objective messages about the merits of a product are quickly lost. I slogged through 90% shit commentaries and found the ones that actually tried to be objective, usually user comments about their daily use cases. "Tell me how you use it for an entire day." Don't talk about benchmarks and that crap.
Most of Surface's struggle was a perfect storm of incompetent marketing with incompetent commentators spinning the wrong things for the wrong reasons, and timing. And yeah, Microsoft did not do itself any favors by releasing the RT first with buggy Office "preview" software that bogged down performance, but I understand why they did so with the holiday season. It was basically the wrong gamble.
From the mobility perspective, I'm all about ultralight, minimalist traveling whether on a 6-hour flight or going to the nearest coffee shop for a day of writing with video/game breaks. So the 10-11" space is perfect for me, but that also directly relates to overall weight, and then battery life is the trick when you get into miniaturization engineering. An extra inch and pound can literally be the tipping point in mobility comfort when you're lugging across an airport, running late to the next meeting, or tromping across campus with three additional textbooks. As for the Pro, what I've reiterated in other posts is that it's supposed to be a primary device compared to the RT; most of the time you would have an external monitor hookup. I think screen size for long-term mobile use is more critical to the RT.