On account of extended RTT, IPv6 (or IPv4) isn't practical outside of the proximity of Earth (including satellites in orbit and the Moon). Mars, at its closest, is about 12 minutes one-way. A 24 minute RTT (1840 seconds plus) won't work.
Any interplanetary protocol must have forward error correction and not require acknowledgment of individual packets or session parts. We will have gateways to interplanetary nodes, but their transmissions away from Earth will not be part of IPv6.
Enough of this foolishness.
Humor aside, IPv6 and IPv4 work perfectly fine in these situations because they are completely stateless. There's no guarantee that your packets will arrive intact, in order, or even at all, but that's not IP's job. This functionality belongs to the higher-level protocols such as TCP (which merely sits on top of IP in the network stack to provide conveniences such as sessions, ports, reliable transport, and in-order delivery).
You're quite right that protocols will need to be radically redesigned with interesting error correction schemes and ACKless transfers, however IPv6 can be used unaltered if we choose to cling to it. TCP, on the other hand...strictly a Terrestrial Communication Protocol. A new solution will be necessary.