Could you see a cartoon rocket ship in use at some central bank or in a press release from a national monetary authority?
Yes I could. Why not? I don't understand this argument at all.
That's like saying Ether is a bad name for a crypto currency because it's associated with dungeons and dragons, magic the gathering, and other kid's games. It didn't stop Ethereum from getting major partnerships.
The main weakness of the rocket logo is that it's not propriety. Rockets are used for many things. Something like the Nike swoosh is completely original. It's tied only to Nike. An original that's established will often be more effective than something that's not propriety.
The downside with something completely original is that it takes a long time and a lot of money to establish. Nike has spent major bucks, but now if you see the Nike swoosh it will often conjure up feelings of being a number one athlete.
To build a brand that would conjure up equal emotions to seeing a rocket, that's a tough one. The one crypto currency that has done it is Bitcoin. It's an original named tied only to itself, just like the Nike swoosh.
Ripple does have a brand that's tied to emotions as does Ether. It seems to me this will give Ripple the upper hand over Stellar. Stellar makes me think of the nerdy kid in school who really excels. Ripple makes me think of when I was a kid fishing with my dad, and I threw a rock in the pond. Ethereum makes me think of when I was a kid and played Magic the Gathering. Bitcoin makes me think of digital money, like electricity running over computer wires or something.