These are just suggestions, not laws 
Ok, what about this: 1. If there is a clear interest from a local or global community to forgive a permaban for some user (voting for example, if more than 20 members support the removal of permaban
Who will decide if alt accounts are vouching for banned alt account? 20 accounts might be 5 individuals. Or 1. Or 20. Or vouching for any other reason/gain? You will need only 1 account with very good argument.2. If at least 6 months have passed since permaban
What was the reason for plagiarism? Was it intentional?3. Just in case of plagiarism
How many cases? 1? 2? More?