This will no doubt be overshadowed by Generics, but Workspaces[0] are going to be incredibly useful for companies using a monorepo with shared packages.
Finally! Helps with both monorepos and multirepos, as illustrated in the tutorial you've linked.
(After going through a bunch of associated docs, I'm under impression that their quality is going down, slowly. At least when comparing it with the stdlib docs' quality.)
Once again, great job to the Go team!
[0] https://go.dev/doc/tutorial/workspaces