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.