If you're designing a language it's probably okay to have string literals that can't contain certain characters, so long as there is some other way to do it. It's a bit different for a serialization format.

The question is what you do when you're converting some data from some other format (for example, dumping a database) and there are strings that actually contain these special characters. Even if it's a bit ugly, it's good to have some way to represent the data so that it can be read back in again without any loss. In this kind of tool, you can't just say "don't do that" because the data has already been saved - you're just converting it. (So my idea of not calling it a string type probably doesn't make sense, on second thought, if you want to be able to interoperate.)

Square brackets are an interesting choice. If you just want to do simple lossless escaping, it doesn't seem that hard:

\\ means a literal backslash \] means a literal ']'

Anything else gets written as-is. (But, what if the database actually does contain control characters in some of its strings?)