But I would love to see a message like this on the profile of a banned user.
This user was banned for plagiarism, see reference
I tend to agree with this but I think it's impossible to include the reference.
AFAIK, the reason for the user getting banned is that the thread is usually deleted already, I don't think how to track the reference but I think the reason could be enough to determine the user's offense.
BPIP extension on your chrome will easily spot banned users but you'll not see the reason for it. When I saw a banned user on the top of their profile, all I think is plagiarism, not ban evasion.