Additionally, Gershwin is the name of the intended follow-up to the cancelled Copland project.

That was not intentional but just a coincidence actually. I came up with Gershwin as something to be comparable to "Darwin" as a core OS. I originally wanted to combine the Linux kernel with a Userland "familiar to switchers" more like a BSD and build on that. I also decided early on it was best to focus on being a DE that could run on anything and make the underlying OS not matter as much. Everyone involved really liked the name, so I went with it.