Indentation languages in general are a step up from editing raw HTML; by the time people are ready for another abstraction, the common tags will be far more ingrained in their heads. Syntax highlighting helps, too (existing solutions for the Slim templating language are already pretty good for Emblem, even coloring unrecognized html tags). And last but not least, you can optionally prefix your html tags with % to be explicit, and prefix dynamic "mustache" content with =.
