Pedagogical pros and cons of requiring undergraduate students to follow open/reproducible research practices?
I applaud your willingness to further your student's contributions to open source. 

There are lots of pros:


Build student's reputations (ancillary to professor and institution)
Create value for society
Students will have an even greater stake in code they know will reflect on themselves, and as a result will go to greater lengths to ensure they demonstrate learning and excellence.


Con:


Students (and stakeholders) may not wish to publish because of fear of negative impact to reputation.


Well, masters' theses and doctoral dissertations are, in most institutions that I'm aware of, are all supposed to be bound and stored accessible to the public, even if the public never reads it. 

In all likelihood, the bad stuff will get rarely read or used. The good stuff will never get enough attention, but it will get far more than the bad. 

Conclusion

It's a risk worth taking, but bounce it off your department head and be certain that they agree. They may decide that since they're undergraduates, it's unfair and not proportionate to require them to publish. Or they may insist that the requirement appear ahead of time in the course catalogue description.