Grim Awakening - 10 man Death Raid is currently being built.
Hardmodes for Frozen Tempest and Endless Eclipse have been on the PTS for a while now and are getting close to being released (not that many people here will ever do them.)
Given there's only been ~10-15 guilds who have cleared all current content I don't see the need for another 20m any time soon, give it another 3 months.
Iirc Trion said they probably wouldn't make an instance as big as HK again, it takes people too long to complete if they have to spend almost 2 nights every week doing farm to get to their progression boss. I think they're aiming for tiers that are ID or FT/EE size, around 8-9 bosses rather than 11.