Is iOS 9 built for the iPad Pro?
Without the right software, even the best-looking hardware is a brick. It's clear many of iOS 9's features were developed with the iPad Pro in mind. Specifically, Slide Over, Split View and Picture in Picture really take advantage of the larger screen. I've found I can be as productive writing on the iPad Pro (working with Safari on one half of the screen and Pages on the other half) as I am using a similar setup on my 15-in. MacBook Pro.
The only caveat is that software needs to be able to take advantage of the bigger screen. This isn't a problem for built-in apps from Apple, but third-party apps need to get on board. The best example is Facebook; the current iOS 9 app simply scales up content to fill the screen, wasting a lot of space. Viewing Facebook in Safari is a better option on the iPad Pro.
There are other benefits to the larger screen: the virtual keyboard in landscape mode nearly imitates the spacing of a physical keyboard, which allows for easier 10-finger touch-typing. The virtual keyboard also has room to accommodate a number column above the traditional letters, saving a screen press whenever numbers and punctuation are entered. There are also buttons for more functionality like font selection, text formatting (including options for smaller/larger/bold/italics/underline), and paragraph formatting.
Another feature introduced in iOS 9 makes it easier to use the virtual keyboard as a virtual trackpad. Placing and holding two fingers anywhere on the screen activates this virtual trackpad, allowing you to drop the text cursor precisely where you need it. You can also use taps and drags to highlight and select words or entire paragraphs.
The enhancements to the virtual keyboard in concert with AutoCorrect and text dictation help make the case for the iPad Pro as a real productivity tool for anyone writing for fun or profit. When combined with optional accessories, the iPad Pro makes a better case for use as a primary computing device.