The chest permissions and promoting to higher ranks they've basically said "not our problem, deal with it yourself". Not sure if they've ever said anything about the room demolition or even the FC Alliance that they mentioned way back in 2.0 I wanna say? But then again, they cut out/butchered so much promised content...

Diadem - DoA
Eureka/4.0 Relic - Horrible, will die as soon as 5.0 hits
World Primal Summons - mentioned, never elaborated after 2.0 release
Housing - Just... so bad... (saying this as someone that owns land)

I'm sure others that pay a lot more attention to panels/Live Letters/etc could add more to the list of forgotten things