I think too 
Letting teams know what they have to change, add,… and giving them 2 days to either comply with the requirements or be disqualified.
Now an other thing is, every team should be aware of those requirements when they sign up to the hackathon. The rules have been published before the application period even started. For some projects I don’t even understand why they are surprised.
For other teams I can understand why they are surprised since there is no clear definition of what’s a significative improvements. @Sirluke and myself have shared our own definitions above. I hope it can help to give a more accurate idea of what a significative improvement is or should be