They are not new challenges, they are the same old challenge that led to version control procedures and systems in the first place: your incomplete or broken code is interfering with my attempts to complete or fix mine!
Whether the broken merge happens in a branch or as part of a rebase is just moving things around. The trick is to enforce good code cleanliness when pushing, whenever that may be.
My team does stuff on mainline and requires a new review on rebase.
My team does stuff on mainline and requires a new review on rebase.