I also think having the capability to sync Dynalist items to multiple Google Calendars can be very useful and practical. For instance, it may be desired that one calendar for ordinary calendar events, i.e. those have a certain duration of time/days, and one as a simple reminder (like Google Reminder).
As the number of tasks increases in Dynalist Next Actions and certain tasks may need to have a reminder, the second calendar, i.e. a Reminder Calendar, can be very useful. Before having this thought, I was thinking about how to sync Dynalist tasks to some task management tools like Todoist. However, I realize that it can be non-trivial (for an average Dynalist user) to achieve this by using the Dynalist API, as discussed in the following post:
Therefore, being able to sync Dynalist items to multiple calendars can be a solution for this use case.