I know it's more than a year later, but I stumbled across this thread while doing research on this to try to create a chart to help my players come up with mechanics for Fabrials for the new Cosmere RPG.
Like Firesong suggested, I also concluded that Midnight and another aether are outside the classic 10 essences, almost like "god-aethers" or something else entirely.
I also initially placed Sunlight + Chach together for the same reason, but came across a potential problem (potential non-problem).
All Aethers/Focuses/Essences also corolate to the color of a polestone (which can vary in color, such as zircon). Chach/Spark corrolate to Ruby/Red.
While I'm not decided, I would also hypothesize that it could be an effect similar to using a magnifying glass to cause heat, and that instead Sunlight Aether corrolates to Vev/Diamond/Lucentia.
Crimson could also easily be Shash/Blood/Garnet.
This is what I've landed on so far, with a heavy part of it hijacked straight from the Ars Arcanum. (EDITTED 2/14/25)
However, I'm not wholly convinced that the Aethers do correlate directly, or perhaps more they have a common root and so have similarities but diverge instead. My brain latches onto the idea of a direct 1:1 pattern because PATTERNS! but it might not be so (EDIT: And Sanderson has said as much)