I'd like to allow users & staff to create posts that embed rich / interactive content, currently the embed tool works to transform some services (like YouTube into videos), but for unknown sources it'll default to a rich card preview / link to the content. With whitelisting URLs it would allow users to paste content into the embed block in a post from a URL, and would then put that into an iFrame. Ability to customize width/height would be nice but not required for MVP.