The ability to merge tasks is now available to everyone.
To merge one task into another as a subtask, simply hold down
on your keyboard, pick up a task with your mouse, and drop it onto another task. The task will be merged in as a subtask and maintains its notes, planned time, and integrated information.
Tasks from integrations:
Tasks from integrations (e.g. Gmail, Todoist, etc) can be merged as well. When merged as subtasks, they will still be fully integrated, synced tasks from their originating tool.
You can merge tasks directly from the integration panel rather than needing to first import the task to your task list.
Subtask actions:
When hovering over a subtask, you can use some keyboard shortcuts previously reserved for main tasks, such as
to start the timer,
to open it in its originating tool, and
to show its integration preview.
You can also revert the merging of a task by hovering over the subtask and clicking "convert to task".
See it in action here