IKEA Tradfri colour bulbs now available

They do all work this way after losing power, including IKEA ones. However they come on at the last brightness. The reason being most people still have a physical switch which cuts the power to the bulb. When you switch it back on it's important that the bulb comes on, otherwise you would lose the failsafe of using the original switch. Some Hue apps have a function to handle power cuts but I don't know how successfully. As to your other point, the Hue ecosystem is definitely the safer bet - everything works well and reliably, and 3rd party support is likely to be superior for a long time to come, but most of the important features are there in IKEA and as you say, Google home support is coming before very long. Unless you really want something it can't do (e.g. program the remotes, sync lights with your TV/music, geofencing) I'd think IKEA would be fine alone. Things could get even better next year when manufacturers move to ZigBee 3.0 so you could always make the move then.

By the way the colour bulbs are not as bright by quite some margin, especially when outputting a non-white colour. The IKEA bulbs also don't have as wide a temperature spectrum as Hue.