We do not have an ETA on the Kage treasure, but as a F2P player, I would recommend thinking about saving up for it anyways. Alot of the ninja that you will be getting in the current treasure packs will be easier to get later on through plot (such as you get Tobi for free during level 70 Plot, and level 80 is one of the pains). Unless you want one of the ninja from Tendo or Sage, I would recommend saving. If you do want ninja from one of those, pick the one you want most.

As for the Kage treasure, the only thing we have been told is we will most likely be getting it before all the ninja that are in it, get put into the game. What they said that means is we would be getting a "temp Kage Treasure" that would be missing any of the ninja that are currently not in our version of the game.

I really hate when people try and correct me with out even asking for a source:

Lvl 80+ Seals (CN to US version)
http://forum.naruto.oasgames.com/en/forum.php?mod=viewthread&tid=4976&fromuid=16848
(Source: Naruto Online Forum)

From Aristeaus when he was a mod:

Itachi Susanoo and Sasuke Susanoo are in the Full Kage pack.

The next treasure we are likely to get is a temporary pack that has Temari 5 conference, Kazekage Gaara, and Killer Bee in it. When the full Kage Pack is released, all 3 of the ninjas are put into the Kage pack, along with a bunch of Kage and assistants, as well as Itachi/Sasuke Susanoo.