I have multiple tasks in a list I call templates. Each has a set of subtasks that are multiple actions I need to complete whenever I get requests for a variety of things that take more than a day to complete. Each task has a hard deadline but there are also intermediate deadlines for the related subtasks. The subtask deadlines are frequently based on the main task deadline. For example, in preparing for a meeting I've been asked to run, I need to have the agenda finished 2 days before the meeting and send a reminder to attendees 1 day before the meeting. I'd like the option to set a subtask deadline as an offset from the main task deadline. For example, I'd set the reminder example subtask above to a deadline of "-1 day" and the agenda subtask to "-2 days". Then if I duplicate the task, which is how I work around the lack of task templates in RTM, and set the main task deadline, the subtasks will also get the correct deadline. This would also be useful for complex tasks I have set as recurring in RTM.

I found suggestions on the forums from others that are somewhat related to this but aren't exactly the same. However, I point them out here as they kind of support this idea too:

Task/project templates (Mar 2017) - https://www.rememberthemilk.com/forums/ideas/21910/

Checklist templates with origin (date Dec 2015) - https://www.rememberthemilk.com/forums/ideas/20491/

Project templates, i.e. sets of tasks for repeatable projects (May 2011) - https://www.rememberthemilk.com/forums/ideas/12780/