As I mentioned. It is a toolkit. You can make it 0-based and then use it everywhere as zero based. You don't need to mix it. In my opinion, it is not worthy it. I just mentioned it to highlight that if you truly want that, you can do it. It was more to show that it is flexible language and that you can roll your own. Not that I advocate doing it.
That sounds like a terrible idea. Both consistent 0-based and consistent 1-based is much better than "0/1 depending on who wrote this part".