With the recent announcement of Neon by KDE, and the rising popularity of Arch, and Fedora trying to get more modular (with multiple release versions) I can't help but feel the market is way oversaturated, but everyone is bringing something to the table better than everyone else. If we had a unified distro set rather than bascially four reimplementations of the same thing, we could be seeing a lot more momentum towards desktop Linux's adoption.

In general, there are two users of desktop distros:

A. Professionals and grandparents, who want stable, unchanging systems with long support. Think your SUSE Leap, your RHEL, your Ubuntu LTS, your Debian Stable, and kind-of-not-really Manjaro.[1]

B. Enthusiasts, developers, power-users, and gamers(!) who want the latest and greatest software. These are the SUSE Tumbleweed, Debian Testing, Ubuntu-nonLTS users (with a ton of PPAs), Fedora Rawhide, and Arch users. They don't want unstable software, they just want to get new stuff when the makers actually release it rather than have computers frozen in time - which in practice, no other OS actually does.

Nobody else is trying to ship an OS that intentionally holds back upstream released new releases, unless you consider the tiered versions of OSX / Windows / Android like that, except their availability is more based on your willingness to spend money / upgrade your device to get them than them just being delayed.

[1] I think there might be a schism between these two even further - grandparents probably want Neon style desktops just because individual distros are not honoring the release cadences of major projects like KDE or Gnome. Plasma 5.6 just came out and will not be in Ubuntu 16.04 alongside Qt 5.6, despite both fixing a tremendous number of bugs and issues with the desktop. That isn't cutting edge features, that is bug fixes, and I don't really believe in holding back major project releases like KDE or Gnome regardless of distro. Just have a switch to pin it if its corporate. But there is a tremendous lack of communication between upstream when major software projects like KDE cannot bugfix their major userbases at all for years (IE, Ubuntu LTS).

A great comparison would be to the Android world. Google devices see continuous releases for their support periods monthly now, like fixed release distros. Cyanogenmod has daily releases like a rolling distro. Any non-Google phone basically never gets updates and plays Debian Stable. But all of them, when using the Play Store, will upgrade every user facing APK on the system whenever updates are available, because those updates are not Google's responsibility, they are the developers, and users are used to knowing it is the app makers fault when something breaks, not the distributor (Google Play). General adoption of the Linux desktop requires this distinction be made, where developers can both easily offer their software to Linux users and be held responsible when they break it, rather than having everything filtered through distros that will basically throw the baby out with the bathwater by freezing all software because they trust nothing.

But on topic, it seems like we now have a half dozen different solutions to the same problem. Why can't I have a distro with SUSE's infrastructure, Ubuntu's brand and userbase, Debian's community, and Arch's software availability? It is like everyone has their own piece of the pie perfected but rather than us having a whole pie to solve any of these 2/3 use cases (I'd consider the server use case is extremely well provided for nowadays, the only domain Linux distros are doing a good job at, between RHEL / Stable / Ubuntu Server). It isn't even really about different distros for different desktops anymore, since pretty much every desktop is available on every distro - either officially like in Arch / Debian, or through the software universe of Ubuntu / SUSE / Fedora. The distinguishing factors are just the holes the other distros will not fill because they are too busy fixing another problem unaddressed at home.

It does not help that the work is then duplicated across all these projects. Packaging Qt and KDE are a pain in the ass, but there are four release teams between all these distros maintaining those releases independently. There is no actual way to fix this - the Debian, SUSE, Ubuntu, Fedora, and Arch devs have already dug in within their camps - but it is still sad that desktop Linux remains niche because rather than working together and combining the best of everything we have everyone is working on their own thing while the whole is lackluster against the competition.