Interesting. I don’t see any immediately obvious technical reasons why this wouldn’t be possible.

There are languages that include a variety of different programming paradigms (I’m thinking of D). I can’t think of any that support different syntaxes but I’m sure one would exist. However, a language that is configurable I feel does not exist and could be an interesting experiment.

I still do fear however, that any attempt would still not be practical as if you design a language feature that os generic enough to work with/without other features and with different syntaxes then it would not be specific enough to be clearly useful. In other words by trying to support everything it becomes good at nothing.