Better markup DSLs have already been written, which "mingle" better in code: HAML and Jade. Unfortunately reactjs-jade never gained any momentum it seems.

Hyperscript seems like a "reasonable alternative" to JSX. I won't say "better" because you're trading <angle brackets> for `h([ , ])` symbols that also contribute to line noise. And other common pain points like "you can't put an `if` block inside your markup" still persists.