Not sure why people are still debating all these issues. Fact: a group of people came together and plagiarized another companies work and made money off of it. Another way to look at it: they STOLE another companies property and made a profit off of it. Illegal, plain and simple.
As far as a Legacy server idea goes, I understand people wanting one, it's fun playing a game the way you liked playing it. It's fun being nostalgic, hell, I just purchased a game system that came out in the 80's I grew up with to relive some of those old memories. The problem is this: WoWis a game that is continually evolving, it's an unfinished product that has evolved over time, sometimes good and sometimes bad. However, the comparison is this, the old retro games are done, they are a finished product, and never subjected to change.
Blizzard would have to either take away from the current dev team to make and then maintain a Legacy style server, or hire on more people to run it. The issues with either is obvious. The former holds back the evolution of the game and requires more time for new content, while the latter costs the company money. As multiple people stated, there is no way to prove how many people would sign up and continue playing, even with a sub fee, to justify the costs of running new servers.
All in all, I can appreciate people wanting something like this, but the chances of it ever happening is almost nothing.