Leopard (Tick) -> SnowLeopard (Tock)
Lion -> Mountain Lion
Mavericks -> ...(uuhhh...whoops?)
Yosemite -> El Capitan
Sierra -> High Sierra
Los Gatos translates as "The Cats" so it seems like it would have been a nice way to end the big cat naming scheme.
It'd also be kinda funny for them to jab at Microsoft's advertising and have an OS X Mojave, since it would fit with their naming scheme.
I very much preferred the big-cats theme. It humanised the OS in powerful ways, making it an extremely powerful and very intelligent animal that dominates through speed and elegance. Rocks are just dumb and static.
We know that rocks don't have a CNS; if they can self-identify the mechanism for this and their experience is obviously quite alien to our own so it doesn't make much sense to project human qualities onto them without more information.
It is true that the qualities of rocks are quite different than those of large felines.