I have replaced my MacBook Pro with the iPad Pro 12.9". As some here have said, this all depends on what you do and what requirements you have. I still have access to a work PC for those very occasional times I need to do something that I cannot do on the iPad. But for 99% of what I do, the iPad is great and I much prefer the simplicity of iOS. I also love that I can just yank off the Smart Keyboard and use it in tablet mode, or I can keep the keyboard on and use it like a laptop.
Also, if you are replacing a laptop, I would definitely recommend the Apple Smart Keyboard. For the first 3 months I owned the iPad Pro, I did not have the keyboard. Then I just got it recently, and it totally changes the device and makes it much more usable and much more laptop-like. And it takes all of 2 seconds to just pull it off and use like a tablet without the keyboard. All in all, it is a wonderfully diverse computer.