Are you gonna embed a Python interpreter into your C# programs though? Better to use something like dhall that's at least open to being loaded from multiple languages.
Right, which is essentially what Dhall is. There aren't any established "real" programming languages that are restricted enough (non-Turing complete, etc.) to use for this kind of case.
> (I (can't (think (of any though))))
S-expressions are never going to succeed; there are too many subtly incompatible variations going around already, and their fans are unwilling to compromise and agree on a common standard.