If you prefer to ship fragile binary file formats for no reason other than finding it too onerous to define something as trivial as an eight-byte file header, that’s silly, but nobody is going to stop you.

If you’re going to use text-based serialization formats as your justification for the decision, however, I’d suggest you look into all the fun bugs, security issues, and weird edges cases that arise from parsers having to make a best guess at character encoding and file format when all you have to work with is the file extension, maybe a byte order mark, and heuristics over the file contents.