SILE can also read XML or Markdown. I use it for publishing books from Markdown via Pandoc (there are several paths from Markdown→SILE).
And for the record the native SIL syntax resembles TeX at first blush but is actually vastly simpler because it is regular and uses a smaller set of possible syntax variations. If you don't like the look or feel of the syntax you can use something else for your source format and provide your own reader that generates a document AST.
And for the record the native SIL syntax resembles TeX at first blush but is actually vastly simpler because it is regular and uses a smaller set of possible syntax variations. If you don't like the look or feel of the syntax you can use something else for your source format and provide your own reader that generates a document AST.