Kaby Lake is the successor of Skylake, but the release schedule is still unconfirmed. Roadmaps have scheduled mobile chips, including Core M, for Q4 this year, but volume availability might be in Q1'17. Though we all know that the MacBook won't be updated until Q2 next year anyway.
What's expected? A very incremental performance upgrade. Intel had to change its famous tick-tock product strategy as scaling down to 10nm proved to be more difficult than previous nodes, so Kaby Lake is merely a refined version of Skylake. That means single digit gains in the CPU performance department, but perhaps slightly bigger gains in GPU performance, but nothing spectacular.
And no, the mobile SKUs with integrated PCH (like Core M) do not support USB 3.1, so we will still be stuck with USB 3.0 (or USB 3.1 Gen 1 as marketing people call it). Thunderbolt 3 is also unlikely given that it requires an additional chip, for which the MacBook simply doesn't have any space. If Apple wanted to support Thunderbolt in the MacBook, they would have done that already.
So all in all, I don't have high hopes for the 2017 MacBook. There is simply nothing interesting coming in the silicon frontier and the design is too new to undergo any changes. 2018 will be the bigger year when Cannon Lake ships.