Is it okay if Marco and Kelly were each others rebounds?
Personal opinion that doesn’t want to prevent anyone from shipping what they want: no. Would that be something normal and realistic for real teens in the real world in their situation? Sure. Does fiction work like real life? No. What’s realistic is often boring or makes for backtracking in the development of characters. Beyond the moment shared in Lava Lake Beach, the focus of which was mostly to allow Marco to realize important things about his life through the experiences of less important characters (sitcom style!), they are two characters who have nothing to do with eachother, and having them becoming romantically involved would feel to me like a huge waste of time, an extremely obvious way to further delay any Starco developments - because regardless of what is going to happen between Star and Marco now that they both admitted and accepted a crush on eachother, even if at different times, SOMETHING has to happen, and they have to talk about it. Having Marco date the bush lady would feel too much like “we got a fourth season so we need to distract the dorks from talking for some more episodes”, and I wouldn’t like such a scenario at all. “Let the kids have fun love make mistakes date” and all that is very true, but it should always be seen in the context of a TV show with limited episodes and limited screen time to dedicate to the relationships. Marco already did that with Jackie, and he has realized admitted and said in several instances how incredibly important Star is to him,
what good could come to his character from a short arc with Kelly that’d inevitably end with nothing happening for real between them?
I know that I’m sounding incredibly entitled right now, as if I knew better than the writers what this show needs, but it all comes from a dark dark place, where the memories of countless TV shows and characters ruined by patterns repeated ad libitum for the sake of delaying the big events reside, and conflicts that could have been solved just by talking it out for five minutes, but that went on for seasons just for the sake of DRAMA. I don’t want to see this happen to SVTFOE as well.