Specific examples:
1. Podcasting. Still no iOS apps that allow me to use an iPad/iPhone as my portable recording studio. There's an app called Ringr that comes close. It has really good sound quality and is 100% designed to do a double ended podcast FOR YOU. It takes all the syncing work out of the equation and removes the need for Skype. But it also doesn't allow me to use my nice mic because it doesn't support lightning mics, and using the EarPods mic for podcasts results in sub par audio. Ferrite is another good one, but doesn't have built in telephony like Ringr does, so it's useless to me as well as far as iOS goes. It would be my go to for recording the show in the same room with someone else, but I rarely do that. Also, doing super precise editing and post production later on in GarageBand for iOS is a complete nightmare and adds hours to the job. Not ideal. I expect that this situation will be remedied in time. The folks over at Ringr have assured me that lightning support is coming. Once that happens, I could easily record a double ended podcast while on the go without having to bring my Mac. (I would still want to edit it and add things to it later on my Mac, but I don't usually do stuff like that on the go.)
2. Steam. iOS doesn't run Steam or any of the games in my Steam library. And I LOVE my Steam library. Not wiling to give it up.
3. Work. I can actually do my full time job comfortably from my current iPad for a lot of the things I do every day. The other day, I took my iPad with me to work while waiting for my car to be repaired, and that worked out fine. But on days where I have lots of conference calling, screen sharing, and heavy multitasking to do (and no, split screen on iOS does not cover it) I HAVE to have my Mac or my work PC hooked up to my two big widescreen monitors so I can have a million things going on at once. And this is not a niche use case. This is how a lot of office jobs are. Every one of my last companies has given every employee two monitors to work from because that's how a lot of people work these days. iPad Pro would need that kind of functionality for me to want to switch to it full time.
I am by no means a nay sayer of the iPad Pro. I have tried it out several times extensively, and I think it's fabulous hardware. The speakers are amazing, the screen is gorgeous, and the guts seem to be super fast. But it's still iOS, and it's still an iPad. Just doesn't fit as my every day computer yet. That being said, I wouldn't be surprised if this rMBP eventually gets replaced by an iPad Pro sometime in the next couple of years. I'm just waiting for iOS to catch up with what I need to do.