Now that more details are available on zigbee 3.0 and devices are starting to come to market, note that it will only combine the profiles previously based on zigbee pro addressing. That includes ZHA, ZLL, and zigbee green, but specifically does not include the Zigbee Smart Energy profile used in smart meters.
The new 2018 V3 SmartThings Hub will support zigbee 3.0, but not the full stack, as well as legacy ZHA devices. There has been some staff discussion of possibly eventually updating V2 hubs to also support zigbee 3.0, but no timeline and no promises.
Specifically, as of this writing (December 2018) the V3 hub will support zigbee 3.0 light bulbs and switches that do not required “touchlink commissioning” and are not using the zigbee green power structures. But it won’t yet work with some of the Zigbee 3.0 devices like the battery-free Wall switches in the " Friends of hue" program.