Functional overview
See live mockup here: https://s.codepen.io/enalean/debug/615728ad14def79e9b694647c582ce16
There is a "+" button when hovering over cells for a swimlane with children. It looks like the add in place "+" button for Kanban.
When I click it, I get a text input to write the child card's title semantic.
There are helpers under the text input to let me know that hitting "Enter" will create the card and hitting the "Esc" key will cancel and close the "Add-in-place".
If the child card's title semantic is mapped to a Text field (with HTML or text format), the add in place only deals with text content (even in HTML format). This maintains coherence with story #13629
Technical overview
To be defined.