Human Interface Guidelines aka HIG influences Gnome's UI and UX greatly. Gnome is the default desktop for some popular Linux distros including Fedora and Ubuntu.
You can see the current HIG in the above link. Gnome thinks it is too old for this time and is planning to revamp it completely. They even want to change the website were HIG is displayed. While HIG will get a facelift, the HIG website will be easy to use, navigate and will be using the latest technologies at its core.
You can now join the brainstorming process. Gnome forums have a thread on it for the same. There might be some discussions going on in the Gnome Gitlab as well.