The new WordPress editor (Gutenberg; now in core) has a variety of default “block” types, and one of these is an embed block. It works similarly to Onebox — paste in a link and it automatically formats an embed.
Currently, unlike with Onebox, it seems to only work with preset whitelisted sites / link types e.g. YouTube Vimeo, Twitter, Facebook, Instagram, and a couple dozen others.
Rough idea: I’m wondering if it might be possible to add similar functionality for embedded Discourse links in a WP site.
Not sure it’d be possible to extend the core recognized embed types (defined here) to support Discourse, as it looks like these are based on regex domain match and there’s no way to know just from a URL if a site is Discourse.
But maybe this could be incorporated in WP Discourse — extending the Gutenberg embed functionality to automatically recognize and parse for embed any link from the connected Discourse site.
Basically enabling a sort of “reverse oneboxing” so that any Discourse forum topic pasted in a WP blog post / page would automatically display as a nicely formatted embed.