Version 1.2.2 of the Wordpress extension will support excerpts in both this extension and in the core Sticky extension.
It'll be available shortly, let's pray to the flagrow.io gods to pick up the release soon. I'll update the Wordpress extension discussion when the release is up.
Sadly existing discussion won't show excerpts because they lack the first_post_id relationship. It can however be manually updated in the database if necessary. But do not set first_post_id before updating to 1.2.2 otherwise things will break 🙉
