Qt, GTK, and other desktop techs are "weird" little tiny niche skills to acquire, and since desktop dev in general is lower priority these days they're going to be rare. HTML5+CSS+JS with a stack based on React or Ember will draw tons of dev talent.
For consistent look and feel the environment could standardize on a single set of CSS themes (maybe a fork of bootstrap) and a "recommended" UI toolkit (I'd recommend React). Use of other CSS or other UI toolkits is okay, but if you do you're strongly recommended to hold to the style guidelines.
Those style guidelines could in turn be informed by things like Atom, Visual Studio Code, Slack's desktop app, etc.
On mobile web tech based apps are the ugly step-children compared to native apps. They've had their chance I'm afraid. I understand why they should be ruling the word in theory, but it just never works out in practice.
I have been developing green field native applications in the last three years.
It has been a return to sanity after doing around 4 years web dev.
GTK3 yes, and it been constantly changing between minor versions so that most of the people that liked doing GTK2 themes abandoned doing GTK3 themes.
As for /r/linux, i get the impression that their permanent residents are a mix of gamers and "devops" these days.
How is HTTPS even close to X11 protocol? That's like saying a car engine can function as a steering wheel.
BTW /r/linux is not all Linux users.