A lot of open-source doesn't have a process to integrate and follow a design strategy from a designer. A business can mandate that work be done to adapt/follow a given design strategy... for open-source it's often harder to do so... and even then you face the same or more resistance to change.

It took basically a corporate control for Audacity to make its' difficult transition to a better design from its' mediocre one. That said, I'd love to see something modern transformed from The Gimp's core in a similar way. That doesn't even begin to cover what you might want in terms of inter-app collaboration...

KdenLive, Blender, Gimp, Krita, InkScape, Audacity and other tooling, as an example, all use different UI/UX base libraries, and no clean way to cross-integrate features between them if someone wanted to assemble an open-source Adobe alternative. There's no baseline equivalent to even MS/Office's use of COM/DCOM for interoperability.

Good points. Designers need to be first-class citizens whose input is sought early on, not to attempt to make a purse out of the finished pig's ear. RFCs are a venue for this. Designers, for their part, need to share their ready-to-go libraries in all the popular frontend frameworks. The two could also collaborate on developing tools to automate design linting, similar to automated code review programmers use.