With notable names like Ryan McCaffery, Jason Schreier and KindaFunny's very own Greg Miller all posing the question "Who is this console for?", I decided I should do my best to answer the question.
There are a few points that continue to get made and I am going to break them down, demonstrating how self fulfilling of their own answer these conjectures really are. I will do my best to avoid anecdotes and self-serving bias but I will remind you that I am human, mostly.
The most common comment about this systems seems to be the low market saturation of 4K TVs and that there is almost no one who can take advantage of this capability. Putting aside the fact that the market for 1080p TVs was in a similar state when the Xbox 360 and PS3 were released aside, this is an odd argument to make to me. The variety of devices delivering 4K to a TV to begin with, is a short list, and further more, not a list of inexpensive machines. Feel free to give a quick Google search for UHD Blu-Ray players, and you will see what I mean. You may be reminded of a similar situation where people began to buy PS3's because they were the most affordable Blu-Ray player on the market. There is a heaping pile of irony there I hope you appreciate as much as I do. So when you ask the question, who is this console for in terms of people who already own, or plan to own a 4K TV, the answer is all of them. The XOX is a 4K video game machine, Netflix machine, UHD-Blu-Ray machine and every other video service you can think of.
TL;DR The XOX is a simple answer to the somewhat obscure question, how do I actually get 4K content on to my 4K TV?
No Exclusivity / Expensive
Again, another very common conjecture is that their is nothing the XOX will play that the original XO/XOS/PC will not. This certainly will dissuade some people from the upgrade, but not in that "I do not want it" way, so much as a "It is not necessary" way. In the case of the owner of a high end PC, there is actually no real reason to buy a XOX, and I do not think that is a bad thing. Xbox has made it clear, that a Windows 10 gamer, is an Xbox Gamer (outside the reason listed above, if PC to TV proximity is a problem).
That being, said there is something to be said for wanting the best of what is available and the predilection to "future proof". Maybe you do not have a 4K TV now, but the next one will be for sure and that itch, that undeniable itch that gets to the heart of gamers, knowing there is a box that you can have that will just make everything a little bit shinier. This exact notion has fueled the "console wars" themselves, with people being quick to bring up performance, and no matter what we saying, it gets under the skin a little bit when you are not playing on the better box. This that same annoying feeling we all get when we go to buy a new phone, and the old model is cheaper than the new model... but it's not the new model.
It is worth mentioning at least in passing, that the XOX is the same price the XO was on release, which affectively makes it cheaper and I wont belabor the specs, but they are better, much better. PC gamers can testify to just how expensive getting a 4K PC can really be, and a $499 USD price tag is not too bad when you start parting out that build.
TL;DR So despite that you can play everything on the XO/XOS, there will those people who cannot resists the prospect of the better box, the future proofing and the ability to sell their Xbox One S, to take a chunk out of the cost of the Xbox One X. If people can find an excuse or means to get the better box, they will.
Early Adopters / Hardcore Fans
These people are your best friends. Not literally of course, we can be a bit a abrasive in reality, but we are the people who spend way too much money on these technologies so that the price to produce them gets shoved down, and you can then buy it at a reasonable price. There is this threshold of gamers, that although may live somewhere between being content on either the PC or console platforms, we stick to one or the other for varying reasons; maybe both. All the same, we get excited when that shinny new thing comes out, and we buy it not because we need it, but simply because we want it, and we can. There is nothing complicated about this, it is just some people's passion to be on the edge of tech, and a lot of us happen to be passionate gamers as well.
TL;DR Some of us just love gaming too much; we are to invested and will readily buy the better box because it's fun and we just can't help our selves.
In the very least, I hope this gives you some insight in to the mind of someone who fully intends to buy an Xbox One X, as soon as preorders will allow.
B.A. Political Studies
Computer Systems Technologist