If it's different codebases, you can do that in almost any language. Have some comebases write fooBar and others write foo_bar or whatever, whatever each one prefers. It's not very good even in that case, because you'll often have to read somebody else's codebase (which is why people praise go fmt and organizations have coding guidelines), but at least there it's OK.

But if you're talking about FunctionName and functionName and function_name in the SAME codebase (and obviously you do, since for the previous case you don't need Nim at all as I said) then that's were madness lies -- willingly impairing yourself to identify optically a symbol to be the same as another or not, because it can have 20 variations...

I've never found this "flexibility" and bike-shedding that ensues useful in any language. I'd even prefer a fixed brace style, even it's not the one "I like". It takes a few weeks of familiarity to learn to perfectly see a different formatting style and even "like it".