It's fun to see new waves of Linux UI polish attempts (like DHH's Ubuntu/Arch scripts, or this project). The Linux desktop could use some care -- and it's the kind of work a single (talented) person can actually do.
The harder problem is the underlying drivers and app ecosystem. Will some third-party package actually run, or will it require qt-2 and then crash on launch? Why is the laptop's webcam upside down, or why is wi-fi dropping every 11 minutes?
One-man distros rarely fix this (unless the person actually has same trouble). It takes a company, that would be willing to invest the sheer human-hours. We had Red Hat, Ubuntu -- companies that did a lot, but eventually capped their investment in the desktop. We need a new one. Until then, we'll keep getting the same experience under a new label.
Obj-C apps are not deprecated yet, so the approach in that GitHub repo must still work. That app is indeed written in C, but a big chunk is about building Obj-C classes and using other Obj-C objects - so it’s not quite C. You won't get much performance benefits or additional flexibility this way.
C is Turing-complete, so you can technically write anything in it. But on iOS, you'd need to build your own C library for application-level Apple SDKs, since Apple doesn't provide one. For simple apps (like small games or toy utils) - a minimal wrapper in Objective-C or Swift could be just a few hundred lines.