I installed the alpha from 17th of April just now. 6RD is still not working, but it does not seem exactly the same either. A few examples:
A promising log entry:
php: rc.bootup: ROUTING: setting IPv6 default route to 2a01:79d:3e85:a408::213.167.115.92
But:
wan_stf is gone from ifconfig, and no ipv6 config apart from fe80 (local link) addresses are seen.
The IPv6 address is gone from status | dashboard | wan.
These two last problems are probably related to 6rd failing on creation, I have posted this issue in https://forum.pfsense.org/index.php?topic=75707.0