The 300 series is expected to include the Z370, H370, H310, Q370, Q350 and B350 chipsets, unless Intel changes the naming to make it look less like what AMD is using. The latter currently has the X370 and B350, which is very similar to what Intel's next-gen chipsets would normally be named like.
It seems the 200 series will be another incremental update, most of the basic feature set is similar to the 200 series but there are two big changes. First up, the 300 series will reportedly get integrated USB 3.1 Gen2 (10Gbps) support. This will enable motherboard makers to provide up to six USB 3.1 ports without having to use separate controller chips. The other change is that the 300 series will get native Gigabit 802.11ac WiFi (plus Bluetooth) support. As always, the exact feature set depends on the specific chipset and the motherboard implementation, what you see below is more like the maximum that's possible with the top-of-the-line Intel chipset.