Apparently part of the issue for the original filing to reveal this information was that some copyright holders are getting antsy that as the case drags on, they won't also be able to file civil cases against Megaupload before the three-year statute of limitations expires. However, as Megaupload's lawyers point out, there is no urgency here since the government itself made no move to share this information over the past two years. If it really wanted to share the information it had ample time to make the request and allow Megaupload's lawyers to review and take part in the process, rather than trying to route around them entirely.
I'm guessing the recent successes against IsoHunt and Hotfile may have contributed to the timing as well. The MPAA pretty clearly thinks it can use those two cases to go after Megaupload as well, outside of the criminal case which will continue.
"I have to admit that I'm consistently amazed at just how badly law enforcement in both the US and New Zealand appeared to screw up the raid and the case against Kim Dotcom. I've said it a few times before, but it really feels like authorities in both places actually believed the bogus Hollywood hype being spread by the MPAA about how Dotcom was really a James Bondian-villain, and acted accordingly, while ignoring any evidence to the contrary."