Going for a current Skylake based system will give you a viable upgrade path for at least another 4-5 years. Skylake, Kaby Lake, Cannonlake, Ice Lake, and Tiger Lake will all use the same 1151 socket, taking us right through to around 2020. Chances are good that we won't see another socket change until Intel releases its 7nm architecture sometime around 2020/2021, and even then that isn't remotely concrete.