This is a bit of a surprise, but it appears that ZTE is working on their new custom UI for their flagship devices, and that's MiFlavor 3.0. This is surprising because ZTE had said that they were going to be sticking to stock Android, and this is nowhere near stock Android. It does look a lot like Huawei's Emotion UI, and MIUI which are both really popular over in China. I doubt that we'll ever see this UI make it over to the US, unfortunately.
While it's not stock Android, it does look really clean and flat. I actually kind of like it. It kinda looks like a mix of iOS 7/8 and Android. Which isn't the worst thing in the world. And exactly what you'd expect out of China. There will be a beta version of this ROM available in early 2015, for those that want to try it out.
In this ROM, ZTE has all kinds of theming going on. Where you can do your own themes as well. Which is always nice. They also have a very comprehensive set of photo editing tools baked into the ROM. There's also a sweet notification shade, although it reminds me a bit of Samsung's. As it has the row of toggles, and the brightness bar there, before you get to your notifications. So it does end up taking up a bit of space there.
All in all, I think it looks like a great UI. It may not be for everyone, and we'll have to wait and see how good functionality is on this one. I doubt that we'll see this outside of China though, as this appears to be for their flagships, and those always remain in China, unfortunately. How many of you like what you see of MiFlavor in the screens below?