Nobody, you got that all wrong. 802.15.4 and 6LoWPAN are established, quite mature standards. HomeKit is the (proprietary) challenger, that adds nothing but an ecosystem for Apple to profit from
Edit: What about Zigbee? Google Home? WeMo? And new to me, Bluetooth Mesh.
Almost all the mentioned standards are based on IEEE 802.15.4.
The difference between 6LoWPAN and and the rest of the mentioned "standards": 6LoWPAN is IPv6 "adapted"/compatible. Thread is based/extends on 6LoWPAN, and adds several missing features or replaces some parts, because similar to conventional Internet devices, you need something more than IPv6 to get things going.