Genuinely, if he's going to have a cryptocurrency to use on Mars it's going to be Nano or some improved version of Nano. This is a guy who reasons from first principles, he's going to look at mining cryptocurrencies and conclude that there is both centralisation inherent and that there could be security mechanisms that settle far faster and with less resource expenditure. To add to that:

Musk hinted during a 2016 interview that his preference for a Martian government would be one based on direct democracy and said that "it would be people voting directly on issues".

I really think that if he ends up pushing some cryptocurrency to use on Mars, it's not going to be one that is for meme purposes, or one "just because it's one of the earliest ones", but it's going to be as he's always done - start with what a perfect cryptocurrency would look like, and then reason from there. And in that case, he's not going to settle for less than constrained by lightspeed, without fees, with a democratic voting mechanism that leads to decentralisation, has low energy expenditure, and that scales using whatever resources are available.

And if he wants to meme aspect, there's always Banano.