Yeah, the ol' "just because we can, doesn't mean we should".
It will be interesting for sure, even from a story telling perspective. Moments of peace and calm are never interesting, and that's why think that if Star and Marco do get together in season 4, it won't be pretty. Maybe in the end, for the cliché happy ending, but in regards to all the things we mentioned, I think they might have trouble getting along.
I mean, we saw way back in season 1 that they sometimes fight throwing harsh words like "sometimes I wonder why we're even friends". They might make up very fast, but the polar opposites will spark conflict soon after. I'm interested to see how the writers will handle this.