I wonder if Gems always sacrifice their physical forms when mating with humans/other species. It seems like fusion is essentially Gem sex, with the downside of population dwindling if the fusion decides to remain together. Kindergarten is necessary to replenish the Gem population, since they can't naturally reproduce, and the culture of fusions combined with frequent wars depletes their numbers quickly.
It raises a slew of very interesting questions: If Steven dies, can Rose return to her true self? What happens when Steven has kids? Why can Steven fuse with Connie, a non-Gem? Would Gems even be interested in mating with human men if the children are all hybrids like Steven and not pure Gems?
(Note: None of this explicitly relates to the current episodes, so there are no spoilers.)