I'm joining the iPad Pro has replaced my MacBook crowd, but with a rather large caveat: I still have a Mid-2015 15" rMBP. It's replacing my 12" MacBook only.
I think the iPad Pro has made huge strides forward in becoming a potential laptop replacement for a good number of people, but as has been stated in here multiple times, it's still a tablet. That being said, I think the computing industry in general is moving more towards a tablet + phone is mostly all you need for most tasks. However, a traditional laptop or full desktop computer is still required in order to enable these devices to accomplish this via application development, and generally speaking, tablet / iphone apps are still underpowered compared to their full computer equivalents. However, I believe the iPad Pro is a device that will begin the transition to more powerful applications that can challenge the full-blown computer equivalents. The specs of the iPad Pro (both in the screen size/resolution + impressive SoC) and it's future generations will continue to open the door for this.
My industry speculation aside... here is the reasoning behind the iPad Pro trumps rMB for my use cases.
I write a lot. I have the Apple Smart Keyboard for the iPad Pro that I'm currently using to write this post, sitting on my lap as I relax on the chaise part of my sofa. I was originally worried about this configuration not being stable enough, especially considering this is my favorite and most common writing position at home. Turns out it's just as stable, if not more. The Apple Smart Keyboard actually provides a relatively sturdy base on every surface I've used it on so far, including my lap.
I do love the 12" MacBook. I think it's revolutionary in it's design, function, and specifications when considering how portable it is... in my opinion, it's well beyond the defined "UltraBook" ... it packs a TON of power in an impressively small footprint. I have nothing bad to say about it. The only reason I'm replacing it with the iPad Pro is for the touch and pencil capabilities; allowing me easy and convenient methods to mock up, design, draw, annotate, and take hand-written notes. The MacBook, while a good keyboard-only note-taking device, can't compete with the iPad Pro in this specific use case.
While I'm not much of a pixel manipulator or gamer, I think it's still worth mentioning that the iPad Pro offers a bit more in this area as well when it comes to GPU performance. So far the iPad Pro has provided a better experience than the MacBook 12 in this realm, but this is certainly not a deciding factor for me and holds very little weight in my decision.
My list of computing devices is ever-evolving as new features become available. Right now (from smallest to largest) it's Apple Watch -> iPhone 6 Plus -> iPad Pro -> 15" rMBP. While this setup is pretty new to me with the addition of the iPad Pro, I'm pretty excited about it and it has worked pretty well so far to provide a nice and complete computing environment for me and my specific use cases.