IPv6 is now available as an option, you just select it in the preferences pane.
Unfortunately only one of the test servers (in Michigan) is native dual stack so the test is then fixed to that location. In addition the latency pinging during test is stays as ipv4 traffic, until I setup a web socket server on the ipv6 server.
All the amazon google and other cloud servers do not support ipv6. They do support it as an edge network feature, like as a load balancing front end, however the test needs custom server software and custom code, and using a cloud proxy that must then talk to an ipv4 test server inside the cloud is rather useless. It should be native all the way. So until I get more native ipv6 servers, one location it is.
Nevertheless as a proof of concept it works. Using the hurricane electric ipv6 tunnel from my australian non ipv6 ISP, I get about 80% of the speed that the local sydney ipv4 test server would give.