[lambda_obrien]

It's hard enough to understand a codebase, but if a language was like Haskell for instance (you can enable certain extensions in Haskell with a flag at the top of a file), you could have a line at the top of a file defining that this file is 0 based, while maybe the default is 1 based for the language. It doesn't seem like that much more than you already have to consider in many languages.

[mixedCase]

Funny you put it like that, because the fragmentation regarding language extensions is frequently discussed as one of the biggest issues affecting real world Haskell.

[tome]

It's mostly talked about by people that don't use Haskell! In practice it's not really a problem.