They've had more than enough time based on what? This is something Apple needs to be thoughtful about. It's not something that should be rushed. What exactly does a more powerful iOS for iPad mean? What does it look like and how is it implemented? Some people want iOS to have a pointer so they can use a mouse/trackpad with it. But is that the right way to go? Apple TV doesn't have a pointer yet I always know where I am on the screen. It uses something called the focus UI engine. That's something a developer also discovered is in iOS 9.1. Perhaps Apple is working on bringing that to iOS devices. Should there be specific enhancements to iPad that are just for iPP? Should developers be able to build apps specifically and only for iPP. Apps that are more expensive and allow for trials and paid upgrades? I'd rather Apple take their time, think these things through and get them right. Even if it means the iPP right now isn't fully baked. The majority of this is software so it's not like people will be forced to buy a new iPP to get these experiences. I think the A9X chip along with the 4GB RAM means consumers will get many years of use from this device. I don't think any app is currently pushing this device to its limits. There's plenty of headroom.
Based on the time iPad Pro hardware would have been in development!
A more powerful iOS looks like a combination of iOS and OS X! It is implemented as touch only with heavy focus on gestures to navigate the OS such as those found using a trackpad on a Mac, but incorporates a point and click solution if one pairs a mouse or a trackpad! It also has the option of the Apple Pencil. This covers the field.
Going back to what it might look like, I would bet it looks like a version of OS X that only allows fullscreen and split screen apps and doesn't include the traditional round corner buttons. The menubar is reworked to accept downward swipe and holds to navigate, much like forcetouch on the iPhone, speaking of which, forcetouch would allow for many more OS level gestures! As a result, Notification Center would no longer be accessible from above and moved to the left as it is on the Mac, via a swipe in from the right.
The current multitasking implementation in iOS would now be replaced. Mission control is present via a four finger swipe up and functions as the main window management solution outside of four finger right and left swipes to navigate full screen apps! Four fingers swiped down reveals launchpad and a single swipe up from the bottom reveals control centre as usual, albeit a more powerful one! In mission control the most recent apps are displayed as full tiles similar to on a Mac and everything past the four or five most recently used apps are displayed as smaller tiles towards the bottom of the screen. The dock is not present!
Some OS X apps are used such as preferences and are reworked to be more touch friendly and look like a split between iOS and OS X. iOS stock apps are revamped with more powerful functionality such as the ability to drag the line between panes to resize them, such as those on the left of Mail and Notes.
In terms of Pro apps, they would have to be written for ARM as traditional Mac apps will not work on ARM and nor should they as developers won't want to rework desktop apps with touch functionality and even if they did it probably wouldn't work well... Instead, Apple should port their pro desktop apps to ARM, make them more touch friendly, again like an iOS OS X split, and wait for third party developers to follow suit!
So in short, it would look like a toned down version of OS X. And yes it would be exclusive to the iPad Pro...