I actually did switch from a 2011 Macbook Air (the dual core 2GB RAM, 13" model) to a Surface Pro 1, a little while before the Surface Pro 2 came out. Why? Because, through gradual changes in my client base and their worlds, I found myself spending more and more time in powershell, Hyper-V management and other purely Microsoft centric tasks. So I ended up Bootcamping my MBA to Windows 8 (required for Hyper-V 2012+ management), so it was now basically a PC, anyway. Then, once a guy next to me got a DynaDock with his Surface Pro, I realised I could dock it to a couple of nice, big monitors and keyboard and mouse and it's frankly more powerful than my 2011 MBA was.
So I sold my MBA on eBay (at almost as much as I paid for it, amazingly - incredible resale value) and switched to the SP1, which I am still using. I have pre-ordered a SP3, in fact, because I have been so happy with it (we don't get the Surface Pro 3 in Australia until September). It's smaller, lighter, faster and better suited to my current working life. I also love the pen, as I now spend about 40% of my week in meetings.
So overall, I don't think this is a bad thing - I just don't expect it to get heavily taken up. I think most MBA and MBP users will prefer to stick with what they have. The trust is, I use my Surface Pro like a desktop or a notepad (a literal, paper notepad, not a laptop notepad). I basically never use it as an actual laptop unless I have no alternative but then again, I pretty much hate all laptops, compared to the desktop experience.