html embed is def possible , but using an actual iframe might lead to some performance impacts. Instead what I eventually plan to build is a url unfurling/screenshot tool that I can use on cards with urls
Have you considered adding markdown support to the cards?
Within an hour I paid for premium and have used it to mock up diagrams and workflows at work multiple times. This is a really fantastic tool for non linear ideas & brainstorming. I hope you are able to continue development!
Can see myself using this quite a bit for work.
Are there plans to add more types of cards? Html embed might be quite cool.
It would also be nice to be able to give the connections an angle so they can go around different blocks