This has been on my mind for a long time now and I’m a strong advocate of developers learning to design. One important aspect that I think is worth mentioning is the fact that actual UI design (with a systemic approach) is more about numbers than art. As a developer you can simply teach yourself ranges of „good color choices” or font sizes. While not as „creative” the UI will likely benefit from that lack of creativity.
The main problem I see in shifting too much to the developer side is going a bit away from Information Architecture as part of the UX process.
While research is it’s own beast entirely, knowing UX,IA,UI and Development is probably the best combo there is. The more people with narrow skillsets we put into the path between IA and Dev the worse the end result will be because of communication gaps between them.