I don't know, I think the downsides outweigh the benefits. I don't want to have to secure a bunch more IP-based devices that can talk to my computers. I'd rather they were separated at the radio level, like Zigbee.
Thread is also IP(v6)-based. But in this context, Thread would go a fair ways toward solving stavros's concern, as it means security could be enforced on the Border Router(s), rather than each individual device.