Ah, I wasn't thinking of it in a sci-fi/space exploration context. I guess in a hypothetical far, far future where we have a technology that allows us to explore outside our solar system (and we didn't destroy the planet too much with climate change), then yes, a different flag may be warranted.

Personally I think an 'earth' flag is more useful as a symbol of us all being in this together, on a single planet that we all share. Obviously there's only so much a simple flag can really convey or impact, but I think it's nice to imagine a future where there are no borders, no nations competing for resources, and less divisions amongst humanity as a whole, so that we instead work toward a more collaborative society. From that lens, I think it'd be a nice flag.