Here is what you can expect:
1) Possibly a single extra hour of battery life;
But, this is unlikely.... in reality Skylake (the next CPU architecture intel uses after the one in the current macbook) is a mixed bag in term of an "upgrade" from Broadwell Core M. Broadwell has FIVR, fully integrated voltage regulator.... which was introduced with Haswell in 2013 and is genesis for the doubling of battery life between 2010 and 2013. Now, the Israeli hacks at Intel's Hafia design warehouse couldn't figure out how to get that to work properly, so they just tossed it out the design. This has the result of drastically increasing baseline power usage, which is why every single skylake KU uses more power than the corresponding Broadwell SKU (same freq, more power usage). Skylake does provide improvements in terms of load power usage at high clocks, for example if you overclock broad well and skylake to the same very high clock the broad well cpu will use more power, and the graphs of power consumption vs frequency are parabolic and steeper with broad well. That doesn't help people using 1.1-2Ghz laptops though.
You might now ask: "Well if skylake doesn't provide any architectural improvements in power consumption then how exactly is the laptop going to have an hour better battery life like you say?".... The answer is simple: Every single other component in the laptop is using less power now... the SSD, RAM, everything uses less power. That's where the real battery life improvements come from.
The only real benefit you'll see from skylake is maybe a visible improvement in GPU, but even there you have issues. Skylake is plagued with bugs, many games won't even run. I don't personally care about games, but even so... the idea that intel is going to somehow replace all dedicated graphics solutions with their own integrated stuff is ludicrous.
2) A much nicer screen... possibly with the DCP-3 perfect color gamut you see on the iPad pro.
3) Better connectivity, possibly with newer bluetooth or wifi specs.
4) More storage options, along with the possibility of faster storage (although the current SSD in the mac 12 is very very fast)
5) Alpine Ridge TB3 controller, which will be a huge help to the current TB2 connector that is used for all connectivity on the Mac 12".
6) Lower price
All of the people talking about 20% or even 10% Cpu are totally full of it, because even though skylake is ~2.5% faster overall than Broadwell, it also runs at 100-200Mhz lower frequency. Remember that 1.3Ghz macbook? Say goodbye to that, the fastest new sku will be 1.2Ghz... and remember the base 1.1Ghz? Well, say hello to 1997 again because your new clock is 900Mhz. Just enough to be able