illumos gate

Currently it's impossible to set a static default route for IPv6.

in.ndpd must always be running, to get the link-local address (fe80::), this unfortunately also pulls in a auto discovered default route with a metric of 1.
So even if you add a static route (also metric 1) it's a hit and miss which route is used.

$ netstat -rn -f inet6

Routing Table: IPv6
  Destination/Mask            Gateway                   Flags Ref   Use    If
--------------------------- --------------------------- ----- --- ------- -----
::1                         ::1                         UH      2   43396 lo0
2001:470:7ee7:30::/64       2001:470:7ee7:30::130       U      10 2053600 net0
fe80::/10                   fe80::222:6ff:fe02:3001     U       3      11 net0
default                     fe80::215:ff:fe05:d7c3      UG      2  360409 net0
default                     2001:470:7ee7:30::1         UG      5  497526 net0

$ route -p show
persistent: route add -inet 0.0.0.0/0 172.16.30.1 -ifp net0 -static
persistent: route add -inet6 ::/0 2001:470:7ee7:30::1 -ifp net0 -static

There is no way of removing the fe80:: default route, if you do it eventually comes back