The new zone, Miragul's Planar Shard, is an x4 epic level raid, which means that it will require four groups of six people to complete. The raid is linked to Norrath through Everfrost through the same door that starts the other Miragul instance. The raid will offer a challenge to all players who enter its halls, but skilled groups can choose paths that will increase the difficulty of the instance even further.
If you're an avid EverQuest II player and can't wait until Shards of Destiny is unleashed on the live servers, you can choose to take a character to the test server to try out the dungeon beforehand and even get a free title on your non-test character for it!
Instructions for signing up for the dev-lead raids can be found on the EverQuest II forums. Raids are being scheduled on Monday, Tuesdays, and Fridays at 7 PM ET (4 PM PT) and are first come, first served, so be sure to check it out!