I've heard the "won't always have a calculator" line, but more impressive was the one time our math teacher demonstrated the ability to solve the problem on the blackboard faster than we could whip out our calculators and punch in the numbers.
If I remember correctly, there's already a system tray icon that lets you adjust volume on your current devices. The extension adds the ability to switch devices from that drop down instead of drilling into the settings app.
I feel like vanilla GNOME is intentionally a barbones common workflow, and that extensions are how you customize to fit your needs.
For example, I often switch between desktop speakers and headphones (where the dongle is always connected), and sometimes other audio devices. I installed the sound input/output chooser so I don't have to go into Settings every time I need to switch inputs. It saves me multiple clicks. But I get that not everyone needs immediate access to change audio devices, so why clutter the UI?
I've used both vanilla GNOME and the post-Unity Ubuntu spin on it. In either case I've grown accustomed to the Activities screen, quickly accessing it pressing the Super key, and using it to switch windows and manage full screen apps on different monitors.
If the size of the PR is a concern, maybe the maintainers will allow a staged approach. Create an Issue describing the feature and indicate step by step how you would implement. Then break the work into multiple pull requests.
If necessary, you could introduce a toggle that's switched off by default until the feature is fully implemented.
I've heard the "won't always have a calculator" line, but more impressive was the one time our math teacher demonstrated the ability to solve the problem on the blackboard faster than we could whip out our calculators and punch in the numbers.
She showed her work, too.