pv6 dhcp for more than one wan interface would be nice
You should be able to enable IPv6 on multiple interfaces. The DHCP pools for IPv6 can be derived from one of the externals, but does not necessarily have to be. In general, we can't run two DHCP servers on the same network.
For this (and other feature requests) I would strongly recommend creating support cases. This will get your requests handled much more quickly and allow you to track them without additional steps.
WatchGuard Customer Support