UX between todo list and calendar

So Sébastien and I are building a productivity app.

It's made up of an infinite outliner (like WorkFlowy) and a calendar. The novelty is being able to associate a regular calendar event with a bullet point. This allows us to set a time-block as a routine (tasks are shown uncompleted the next day, so you can complete them again) or project (tasks are one-off, and you just keep going on the next day).

One of the things we've discussed was how to merge the interaction between the infinite outliner and the calendar. At the moment we're thinking drag-and-drop would be the best option, as shown in our presentation video.

How would a UX designer approach this situation?