When the North American realms came back online after maintenance today, the second Sunwell Plateau gate was open. This means that all you high-end raiding guilds now have a chance to tackle M'uru, SWP boss number five, while I cry softly to myself and work on melting Malchezaar's face off. The first SWP gate was opened after patch 2.4 had been live for two weeks, and the second, today, was three weeks after that. This makes the likelihood seem pretty decent that the
fourth third gate, allowing access to Kil'jaeden himself, will open four weeks from today, but we'll have to wait and see.
Nobody killed M'uru when 2.4 was on the PTR, so we don't really know what he might drop, although four trinkets named "...Naaru Sliver" seem fairly likely, as they are SWP drops and M'uru is a Naaru. See World of Raids for stats on the trinkets and some information on the M'uru fight. The European realms will presumably get the second gate open tomorrow, after their maintenance.