In addition to compatibility with the client machines, it ensures a client which can be made to interact with private servers without worrying about the copyright claims that results from using official clients with patches.

Having an open source client and open source servers could also be the start of fan content. Kind of like how Beyond All Reason completely recreated the Total Annihilation RTS and made it free and open source.

I’d love to see an indie group put together a WoW expansion.