Internet in IPv6 is 2000::/3, not ::/0
Some people think that routing to IPv6 Internet is ::/0 which means everything. This is not recommendable since not all prefixes of IPv6 are allocated to RIRs.
Internet in v6 should be 2000::/3 (reference RFC4291), but not ::/0. This is unlikely to change in the coming 30 years. Do not use ::/0 in making default route.
If I want to add a route to IPv6 world, then :
#/sbin/route -A inet6 add 200::./3 gw 2001:4625::7
Special attention must be paid to prefix 64:ff9b::/96 for DNS6 +NAT64. There should be an additional route to the NAT64 router serving 64:ff9b::/96.