um, crossfaces results in literally half the polycount of a rectangular prism
You would think that, but it's the same. A rectangular prism with no ends has 4 faces. Crossfaces have 4 faces too, they just happen to be in pairs directly against each other.
Might wanna make it a texture for a piano.
The idea behind the project is musical instruments you can reasonably carry. A piano isn't really one of those, but I won't stop anyone from making one if they want to. I do like the "strings are a single texture" idea though. It could resonably apply to any stringed instrument and not look half bad, in fact.
Anyway, I don't really care about the details that much, or how much detail any given instrument has, as long as it suits Blockland and looks good.