There are standards for Home Automation communication out there - ZigBee and Z-Wave. These are the low power communication protocols that home automation devices can use to talk to each other (WiFi is too power hungry and heavy weight). If you take apart a Nest thermostat you can find an unadvertised ZigBee radio buried inside.

ZigBee is an open standard developed by an alliance of device manufacturers. Z-Wave is a proprietary standard developed by Sigma Designs. Both are able to create a low power mesh network for communication between home automation devices. These protocols have been around for a while and are supported by 100s of device manufacturers.

That said, I have no idea what Google/Nest or Apple plan to do. They may be creating their own standards for communication, or they may build a communication protocol on top of ZigBee or Z-Wave.

If you're interested in working with an interoperable standard now though, you can buy off the shelf ZigBee or Z-Wave radios, devices that speak ZigBee/Z-Wave, and build your own HA solution. However, I've found through personal experience that interoperability between devices using the same standard is not always perfect. I'm looking forward to the heavyweights getting into the ring and hopefully cleaning up the industry and making it more interoperable.