I’ve been using GNOME for quite a while often times I had to change some things myself, by patching the source code and the building it manually. One of those changes is the addition of a “save to disk” button in the screenshot controls. This allows me to choose if I want to save a screenshot or not, since in most cases I don’t want to save those. I believe there are many people that would prefer it.
So I’ve decided to submit my changes. Now, since GNOME 48 is stable, will new features be accepted? Or should I port it for GNOME 49-rc / master?
GNOME 48 won’t have new features added to it, because as you mentioned it’s a stable release
GNOME 49 isn’t yet stable, but it’s currently in the middle of a feature freeze. This means that no new features will be added. This gives time for translation updates, screenshots to be taken, and release notes to be written
So you should propose the feature to the main branch, which will eventually become GNOME 50