Tithing has already been enforced upon congregations in a way, just not upon the individual publisher
If they ever try to implement tithing for individuals, there would be a great outcry & the subsequent damage would be irreversible. I believe that such an outrageous move would have a reverse effect - where many who give would actually stop giving in protest. I believe that it would also lead to a start in global decline, instead of the decline that mainly affects developed & affluent Western countries
I would actually love to see the organization try to implement tithing. Am sure many would wake up as a result!