I was talking in general about Open Source and design not about Plasma. But since you ask, here are some small things I noticed in the video
- Mismatched visual styles: when you tap the phone icon, you get a bar of three icons. Two are simple line icons (History and Contacts), the third is a detailed picture of a keyboard to denote keypad. A minor thing and easily fixed.
- Interface inconsistencies: I noticed that a large red X is used for closing a screen (which I like over the sometimes unclear Back button behaviour you get in Android). But at 3:16 in the video the Wallpaper screen has a 'close' button (with X) and below that in the tab bar is the larger red X for closing too. So you have two close functions on the same screen. You see the same duplication on the date and Time screen at 3:41. By the way, I think the way Windows Phone lets you change date and time is much nicer. It's a similar spinner approach to Plasma but less cluttered. Here's a video of it in action: https://youtu.be/kIsWgCX7qtE?t=54s
Also, the commands 'close', 'cancel' and 'delete' all tend to use the same X icon in many UIs so if there is no label for X, then it's meaning (and behaviour) should be consistent across the OS.
- Weather app: there is a 'hamburger' menu on the left and another slimmer hamburger menu on the right. They feel too similar visually. Presumably, the right-hand menu is equivalent to the overflow menu you find on Android. But are two menus needed here? Could they not all sit in one menu?
Obviously, this is a beta and these are relatively minor points. I can see some influence from Android, which is fine - there's no doubt that Google, Microsoft and Apple all study and are influenced by each others work. I just hope the OS stands up well as a unique UI rather than just a clone of bits from other OSes.
Overall, it looks quite polished for a version 1.0 and I hope the project succeeds. I would love to see an open source project take the lead in design/UX over existing projects.