> Currently skills cannot be tagged to different models. Ideally we should be able to say -- for trivial tasks, the skill should always use Haiku even if invoked from a session with Opus xhigh.

You can set the model for a skill. You just set model: haiku at the top and it will use haiku! You can even set the effort level, look for “Frontmatter reference” in this doc article: https://code.claude.com/docs/en/skills