Renewable assignments is a great pedagogical strategy which gives life to students projects/assignments beyond their classroom. And I think this is the best method to encourage students create OER too! As in one of my trainings when I introduced this topic and gave example of David Wiley’s “An Open Education Reader” where he and his students collaborated and contributed. I remember this inspired @Malathi and she planned such kind a assignment for her Post Graduate students.
Here I agree with @Eseta -
“The burden of decision-making can be intense if you’re an individual teacher running a renewable assessment.” There are challenges /issues to encourage these type of assignments in place of traditional assignments.
Another project I should mention here, which really motivates me. I am a big fan of a We Like Sharing of TUDelft. With these kind of assignments I think we can not only motivate students to collaborate and contribute to OER, but we can see a real world impact. And it can also work towards help students build their digital skills (for example if the assignment is to write a blog post / edit Wiki article etc.) . There may be some challenges too! Like quality measures. As a teacher we have to make sure that they publish quality articles/work.
And in my personal experience, I always have a doubt that my assignments are considered renewable or not? 
As in my trainings for example when I train my participants on using H5P (
this is my favourite tool) I encourage them to publish one publicly as those activities can be reused/repurposed by others.
In short, I think the concept of #RenewableAssignments is the best way going forward to have quality content available publicly.
Thank you @Florankem for starting such an amazing topic.