What WordPress 4.x Could Be

Mustache may be too limiting for designers, and a custom template language may represent an annoying learning curve. How about Twig which is well adopted within the community?<p>(after a Google search, it appears people have done this integration already)

That was a really dumb idea. Kill off thousand's of themes and anger millions of developers and end users, just for the sake of having cleaner, "purer" code?<p>Better idea: fork Wordpress into something called TemplatePress, implement a templating engine which does not allow for arbitrary php code in themes, and see how well people like it. Chances are it will be dead within a year-- people choose Wordpress because it is easy to modify it to their own needs. They don't care about maintainability or cleanliness or portability.