Here's update on my iPad Pro Laptop Replacement experience

1. There needs to be a change in file usage metaphor in iPad Pro. You no longer can simply move files around different applications easily compared with typical laptop using Windows or MacOSX. For example, it is not a trivial exercise to send multiple format files as attachments in an email or just send multiple file attachments in a single email. There are solutions (from use of another app), but it's so trivial on laptops. My recommendation is to use a File management application like GoodReader or Copied. But you have to manage the files you kept with these applications, and they would take up valuable space on your iPad.
2. There are also differences in the way applications work in Sharing. For example, if I have a PowerPoint file and I want to share it via email, it would not work with my iOS Mail account that is based on an ActiveSync service with Exchange. The draft mail that is created simply does not allow me to choose my ActiveSync account (other accounts from Gmail and iCloud has no problem).
3. Windowing is a big change. If you are very happy working with overlapping GUI Windows, then you are going to have withdrawal syndromes. iPad Pro can only do 2 screens at fixed location. You cant shift any windows around. The key benefit I see with iPad Pro is it forces you to concentrate on your task at hand and everything looks bigger with the single window focus.
4. Some tasks are simply impractical on the iPad Pro. For example, if you need to move slides from different Powerpoint files, you have to go in and out of the file to copy one slide at a time. And there’s no object manipulation in Powerpoint, you cannot select multiple objects to move them around … Correction, Microsoft just added some “pencil” feature in Powerpoint. Now you can annotate slides with your finger or Pencil during “Presentation” mode.
5. There is also the web proxy issue with Office 365, which seems to work best without http proxy. So if your company requires you to use http proxies in internal network, then you either have spotty performance or worst, no connection.

So thus far, I would say it's mixed feelings. The iPad Pro is lighter, uses less power, more agile (rotate screen anywhere) and portable, good for watching video, responsive, and you only need to carry a universal charger for both iPhone/iPad. I believe iPad Pro apps will improve over time, and I hope Apple will add better handwriting support. Now I'm using laptop in about 20% of my work time. I do hope it could be reduced to 0%, one day ....