In the episode Chille Tid, we learned two minor factoids that each individually have big potential consequences.

One: Fusions seem to have head spaces in which their components interact.

Two: Steven can enter gems heads through his dreams

Why is this so important? Gem monsters!

At the moment there is no official confirmation for what exactly causes gems to become corrupted. There are more than a few theories out there, but the most popular theory by far is the Madoka Method: the idea that corruption is basically just what happens when a gem goes crazy from stress, isolation or trauma.

In this case, the gem isn’t physically cracked, which is why Rose’s tears or Steven’s spit can’t heal them, but on the inside they are severely damaged individuals. These two concepts the writers introduced give Steven direct access to their inner self and a way to swap spit with their mind instead of their body.

Both of these mechanics have their ups and downs. Steven wandering into a gem monster’s dreams and healing them preserves the balance and cast of the story since it’s unlikely Steven will ever be able to do this completely at will, but we don’t know if steven can wander into the dreams of a bubbled monster, and unless Centipeetle turns out to be a YD supporter there isn’t much room for conflict

Fusion is, in my opinion, a better bet. There’s no reason it shouldn’t work, and it lends itself pretty easy to a story: Steven fuses with Centipeetle, but she becomes frightened by the sudden change and their combined body goes on a rampage while steven struggles to save the day from the inside. The only question is, is this too easy a solution?

(BTW, I want to thank a few anons on /co/ for their help coming up with this. Most of this theory is their idea, not mine.)