I agree that for concept work, sketches, and even the occasional finish illustration, the iPad Pro might work fine enough. But it remains limited because of its operating system, which AFAIK doesn't allow for user file control and organization. Most apps appear to be stripped down in some ways to accommodate the IOS environment (whether that's due to RAM limitations or other IOS restrictions, I don't know).
One thing that isn't mentioned much, if at all, is the use of fonts in IOS. I remember IOS 6 (or 7, I forget) on my iPad3 had no obvious means of adding or managing fonts. I seemed to be stuck with what Apple installed. As Donald Trump would say, "That's a YUUUUGE limitation!".
I have over 500MB of fonts that I'd like to have access to when I'm working on design, regardless of which Adobe application I'm working in. I don't know if the latest IOS has instituted any font import and/or management capabilities, but that's crucial to making the device a "professional" tool, in my opinion.
Since the thread's been resurrected...
Here's the thing. If the question is, "Will this replace a desktop Mac in an office/studio environment?" then the point is missed altogether. This is a
mobile device. It's not about whether it can replace the studio, but how much can be accomplished
away from the studio.
I spent decades in recording studios and making concert recordings on location. Toss in a fair number of years doing audio in TV studios, 45 years of carrying around a day pack loaded for nature and travel photography...
Studios are controlled environments; large, dedicated spaces with difficult-to-transport gear designed to provide an optimal working environment. Mobile gear (even when shooting a feature film on location with a 100-person crew and dozens of support vehicles) is by its nature a compromise. You do your best in the field, then fix it (if necessary) in post.
Color calibration? Unless you have control over ambient lighting, precise selection of a color profile becomes meaningless. Nobody's likely to work with their iPad under a hood, like some 19th century portrait photographer. For that matter, as a photographer today, I wouldn't make fine color adjustments prior to sending my images to a publication's art director - it'd be pretty dumb to try to anticipate the color balance of the rest of the page layout.
Fonts? Same thing. Presuming Adobe produces full-strength versions of its pro apps, they'll undoubtedly support font substitution. As it is... I occasionally author/revise book manuscripts in InDesign on my office Mac (it's an efficient way to work when you have a tight, complex page design). I don't carry the same, huge font set the art director carries on her office Mac. I have the fonts needed to support those manuscript designs. Occasionally, I'm missing a font or two, and Adobe makes a substitution. Sometimes it looks like garbage, and the art director may have to tweak the layout once she gets her hands on it, but trust me, she'll do that even if no fonts were substituted. No doubt, if InDesign ever comes to iPad, things will be little different.
"Grownup" file systems are made for managing terabytes of data, but mobile devices have significant on-board storage limitations. If this was the age of paper, you'd carry sketch pads into the field, not truck around a room full of filing cabinets. All you ought to need on a mobile device is the current project - that hardly requires more than several levels of nested folders. That's hardly so complex that you can't use a simplified file system like DropBox or iCloud Drive (have you even looked at iCloud Drive???). Yet, we're connected wirelessly to the web. If we need to connect to the archives, we're able to access that entire, massive data store back at the office or on a cloud server. Most likely, there's a lovely, web-based file browser to log into.
So, back to the original premise... It is not whether mobile gear can totally replace the studio environment. It's how much you can do, and how well you can do it, in sub-optimal environments....
If you sketch digitally, do you have to carry a laptop plus a Wacom tablet, or can those two items be combined into a single, mobile computing device less than a third of the weight and bulk of the combo? Will the results be stored as a low-res bmp (no), or can it be stored as a high-res TIFF or vector graphic (yes)? If I shoot in the field, can I edit the images sufficiently that all the art director needs to do is fine-tune after I upload? If so, then a professional in the field has a pretty worthwhile tool.