It was always going to be that way. Threadripper 2 is just Threadripper with the two blank spacers in the IHS replaced with two more Zen dies, and a fab process change from 14nm to 12nm (but not architectural changes). It's very much what would be a "tick" in Intel CPU terminology.
Edit: Plus, the TR4 socket is guaranteed to be supported for 4 years, per AMD's roadmap at https://community.amd.com/thread/226363