Prettier already supported this feature, but it converted empty named blocks to self-closing, which is not supported by the Glimmer compiler.
See: Glimmer's named blocks.
// Input
<Component>
<:named></:named>
</Component>
// Prettier stable
<Component>
<:named />
</Component>
// Prettier main
<Component>
<:named></:named>
</Component>