On the one hand
All of those people building Ages will finally have a chance to really share their skills.
All the people longing to be back in the Cavern can.
All those who need an Empire of their own, with their own rules, can have it.
On the other hand, unless Cyan runs their own canon server, we'll never see the DRC again, never know what happened to Yeesha, and the truth behind Wheely's death and the Bahro cave she found...
They could never have canon plot things happen on any fan run server, not without accusations of favoritism or elitism, demands of proof of Cyan involvement, ect and so forth.
So, while this keeps Myst Online as a game, as a concept alive... the story of Uru is, at this point, dead.
EDIT: Just after poasting this, I saw this quote from Chogon (Mark DeForest) over at the MOUL forum:
By opening up the source to MystOnline, it does not preclude Cyan from creating their own server in the future with Cyan's content and storyline. However, with our current situation, that might be a long ways off and we don't want to hold people back.
So, there is always the glimmer of hope that we will, someday, get the Uru story Cyan meant to tell. Less dead then, and more like Sleeping Beauty.