It would seem that some re-arrangment of current IJN tech tree is incoming, in addition to a new mini-tree that goes only to tier 8.
Kagero, Tier 9 to tier 8
Fubuki, Tier 8 to tier 6
Hatsuharu, Tier 7 to tier 6 (New Tree)
Mutsuki, Tier 6 to tier 5 (New Tree)
This re-arrangement features 4 new ships in total.
Akatsuki at tier 7
Shiratsuyu at tier 7
Akizuki at tier 8
Yugumo at tier 9.