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.
I recall reading that the thread ripper 2 is supposed to use more power so early motherboards with that socket my not be able to handle it. Just something to keep in mind.
Most/all early TR boards were "gaming" branded/targetted, and those typically have power headroom for overclocking. It's certainly possible some of the early boards won't be able to support TR2 at full spec speeds, but I would anticipate most being able to.
2nd Gen TR will draw ~250W. X399 boards have at least 1x 4-Pin and 1x 8-Pin ATX-12V connector, so at least 225W. The rest is supplied by the ATX 24 pin connection. Some X399 boards use 2x 8-Pin ATX-12V connectors, that works out to 300W, which should be more than enough for Threadripper 2.
AMD's forward compatibility is one of the most amazing things to me, so much so that I still can't believe AM4 is going to remain viable for future CPUs for a while hence despite its age.
It's also a big reason I'm not going with Intel, since I know I can upgrade to something significantly better without having to get a new motherboard.
Worth noting that with AMD sockets, physical compatibility is no guarantee that it'll work without a software update. If you're unlucky/incautious during a system build, you can end up in a catch 22 with a motherboard that requires a BIOS update for your new CPU to work, and no way to boot it to update the BIOS because your CPU doesn't work. AMD will loan you an older CPU if you jump through enough hoops, but it's probably less hassle just to buy the cheapest last-gen CPU you can find on Amazon.
Still a better scenario than changing the socket all the time, but it can catch you out if you're used to Intel's "socket = generation" philosophy.
Edit: Plus, the TR4 socket is guaranteed to be supported for 4 years, per AMD's roadmap at https://community.amd.com/thread/226363