While I love having a separate input field to create a teaser, I miss a way to - optionally - having its text inserted into the node when the full node is displayed.

Something like a checkbox added to the teaser field "insert in node". There could be a further option to either insert it at the start (summary/intro) or at the end (conclusion), or even (via some "placeholder" markup in the node itself) somewhere in the middle of it as a pull quote. The teaser itself should then be themed/themable.

Would this be doable?

(I think it probably is, but I'm too new to Drupal to see an easy way to do it myself. If no one else would be interested in such a feature, then I'd appreciate at least some hints for what to change where to accomplish this!)