I really doubt Rose meant to leave Spinel like that for so long. She probably had every intention of going back for her after the colony was established... and we all know how that story went. Rose got caught up in running her rebellion and maintaining her role as Pink. Once Pink was "shattered," there would have been no way for Rose to go get Spinel. Especially if the corruption song happened shortly thereafter. No one else must have known where Spinel was to retrieve her (I assume at the very least Blue would have taken her in.)
I suspect this is the ending theme for the movie with how long it is.
I'm tied between Peridot and Pearl.
Perhaps that might be the plot for the movie?
I do believe the major conflict with Homeworld is now ended, for good. I like to think Rose is smiling, for her son pulling off the impossible. Maybe it wasn't what she planned, but Steven did it anyway. (And I think Steven was right to call out that one of Rose's failings was she just gave up and ran away, tried to pretend she was never Pink Diamond at all.)
Super Bingo, considering everything on that card happened. (Even if the Peridot space was technically just her being as overconfident as ever)
I laid out some possibilities in a comment higher up.
Well, there are stories to tell about the rebuilding of Homeworld. The newly healed Crystal gems adapting to life on Earth (as I imagine the Homeworld aligned ones returned with the other Diamonds). Steven and Lars both have spaceships, so there's another avenue for adventure.
It was written to be a possible place to end it, yes. But they teased that the movie is coming in the fall, and I would not be surprised if they use the movie to set in motion new story arcs. (Because I'm pretty sure if this or the movie was the actual series finale, they would have advertised them as such.
I'm dying. Just about everything on the card happened.