According to Ars Technica, Thunderbolt 3 has a USB-C connecter.
http://arstechnica.co.uk/gadgets/2015/06/thunderbolt-3-embraces-usb-type-c-connector-doubles-bandwidth-to-40gbps/
and supports USB 3.1, and two 4K 60Hz displays or a single 5K @ 60Hz display.
This is what the rMB v.1 is missing, and presumably what the rMB v.2 will have.
https://thunderbolttechnology.net/blog/thunderbolt-3-usb-c-does-it-all
http://arstechnica.co.uk/gadgets/2015/06/thunderbolt-3-embraces-usb-type-c-connector-doubles-bandwidth-to-40gbps/
and supports USB 3.1, and two 4K 60Hz displays or a single 5K @ 60Hz display.
This is what the rMB v.1 is missing, and presumably what the rMB v.2 will have.
https://thunderbolttechnology.net/blog/thunderbolt-3-usb-c-does-it-all