"even the ones without a date."
I think this is very important principle: in the world of fully online courses, many sites are self-paced. Having to rely on dates - especially absolute dates - should never an assumption. As Matthias says, students find this annoying since they still have to hunt for such information. Teachers as well. It may even be better to have no information at all than incomplete information.
Years ago, there was a web site called "Upcoming" which was just that: what do you have that is upcoming to do. Some things may have dates, but many may not: but you still have to do them soon.
I think focusing on "Timeline" as
a concept makes the block really only useful in brick and mortar,
absolute date, group work scenarios. But that is only a small part of the online edu world now.
The real problem you are trying to solve on the Dashboard is give people the overview of what must be done next, what is upcoming, regardless of dates.
For example, if I just did an assignment in section 2, then I must be moving on to section 3. Just hanging the data on specifically set due dates may be easy to code, but is not how many people work (which is why on many sites I support, we just remove the block altogether.)