We really, really need server-side template languages to catch up to, you know, 2014, where components are a thing and you can do this:

<Quote @src={{this.book}} @loc='p. 123'>
Look ma! Content *within* a *component*!

Nunjucks/Jinja macros are the closest I’ve seen and… they’re not even close in terms of expressivity. This is why people build things with React/Vue/Ember/etc. just for server-side stuff: because the DX is miles ahead.