Some fair rebuttals...but I still think Il be passing on this for now. My Air is doing me good and for the cost its just too tempting to get a MacBook or a refurbed rMBP. Im sure it'll be a cool device though. That big screen will make watching shows and reading a great experience.
Everyone's answer will (or should be) different; based on their needs and wants.
As always, it depends on what and how you intend to use your devices. There is little purpose in getting an iPad Pro if you want to keep using it for exactly the same things, and in exactly the same ways as your iPad Air. It would also be unwise to get and iPad Pro if you imagine using it exactly like a laptop.
Now, if you see things that it can do that you've been wanting, (or suddenly want in the wake of being shown what it can do), and your willing to give up the advantages of the other two devices in favor of the new iPad Pro's advantages; then it starts to look pretty attractive, even at the price. (assuming you can't afford, or don't want, one of everything)
That's where I am.
With the iPhone 6 Plus, almost all my ultra portable computing needs have ben met. My current iPad Air is mostly at home now. When I do use it out and about, the things I'm using it for are much more laptop like; meaning a keyboard. A bigger screen and keyboard start to look pretty attractive, yet I still don't want or need all the versatility (and complication) of a laptop. I like my iOS apps and UI. The Apple Pencil is pure candy. I like to draw, and I've always wanted to be able to take 'good' notes with a stylus (yet haven't found a pen/app combo I like).
It's also a respectable replacement for most of the things I do on my iMac. I'm considering not replacing it when it finally fails. Instead I may replace it's entertainment functions with and AppleTV, and do everything else on the iPad Pro. That's a trade off, since some things will be easier, and some things harder. But it's a trade off I can see making, and one that would save me $500 to $700 dollars over getting a new 27" iMac.
Just like the original iPad I'm not seeing what it wont' do for the price, but what and how I'm likely to use the new device, and how it will fit together with my other devises for work, and play. So, I'll be scrapping together the money; though I doubt I'll be able to do so before Spring. Probably not until tax returns.