The thing about the site mentioned is that it already exists, but we fail to accept its reality.
Millions of ebooks have been bought in the last decade, I suspect that millions have been deleted as well, this is a crime against knowledge as you well know.
It is in our nature to maintain the knowledgebase.
If the sites TOS
required you to click a button saying that you were the original purchaser of the book that you are uploading I think that would clear up any confusion in the courts. Not that I would ever attend court, except to debate the nature of the court system itself...
I'm fairly certain that the site will require an active connection to the site itself, cloud reading. That way it is easy to ensure that only one reader is reading the book at a time.
I am not sure why malware writers would want to get involved except perhaps by making their own copycat site with ads (AKA googlebooks).