For me personally, XCode doesn't make a whole lot of sense on a touch screen device with limited screen real-estate. I'd prefer to use a Macbook.
I'll grant you the touchscreen part (though they are offering an overpriced keyboard lid), but not the "limited screen real-estate". They are offering a 12.9" screen. Macbooks have long been offered in a 13.3" size. The iPad will be in a 2732×2048 resolution. I've considered the 11.6" / 12" range to be the minimum for a laptop that could be usable as a real computer (as compared to 10" netbooks). Those 12" laptops would frequently have 1366x768 resolutions. 13"-14" computers are easily usable full time. The iPad Pro's screen is obviously not a limitation. The oversized cellphone apps on it may get in the way, but not the screen.
For working with textual information like you are in Xcode, the native resolution on retina displays is almost meaningless. For example, the native resolution on my MBP 15 with retina display is 2880 X 1800, but the default effective resolution is 1440 X 900 which is the same as the non-retina displays of previous versions. Same with the iPads. The newest iPad Air has the same effective resolution as the original, - 1024 X 768. That's because Apple pixel-doubles the text so it's large enough to read.
You could have a native resolution of 2880 X 1800 on an iPhone but that doesn't mean the screen would be optimal for doing Xcode work.
That being said, the screen size of an iPad Pro is approaching that of an MBP 13 which I used for many years for software development. Before that I briefly had a Macbook Air. Obviously portability is an important feature to me and I could hook them up to external displays in the office. However, when away from the office I found the 13" display to be a liability unless I was just working in the terminal, web browsing, checking email, etc. The latest MBP 15 that I have now is almost as light as the earlier generation MBP 13 and is probably thinner. The larger screen is well worth the added footprint when I'm away from the office.
So I guess I don't see the fact that Xcode doesn't work on the iPad Pro as much of a downside since I don't think it's a great form factor for that kind of work anyway.