Surprised this thread hasn't gotten more hits as this seems to be an important turn of events. If it means that they were so far apart that both sides said it would be a good idea to get a third party in the room, then that suggests all the happy talk from the league and the players was a lot of hot air.
I think it's interesting but inconclusive that most of the positive reaction seems to be coming from the players' side. More power to the players for getting the owners to agree to this, if that is how it went down.
The mediation isn't binding, but, at the end of the day, an unbiased mediator can point out where s/he thinks one side or the other isn't being reasonable.