1- no one can answer you about when his bt will release

2- one thing to say here ( WE ARE NOT LIKE CHINA BECAUSE WE HAVE A DIFFERENT TEAM OF THIS VERSION )

3- he are so good in nine tails like hashirama and he make a good damage to him :D

To answer your questions ..

1. No one knows when the skillbreak of Yamato will be released .. Only the team that works behind the scenes knows the answer about that ..

2. It is good to take reference from other game versions but it is useless too sometimes, CN released Yamato's skillbreaks but who knows if the EN server will ever get that skillbreak .. It maybe not, or maybe the next 3 years .. Only "them" knows the answer ..

3. I have no idea how Skillbroken Yamato works ..

He will be god tier ninja for 9tails for earth and water for sure, with high possibility for other classes too. As for other classes, even though barrier doesnt buff them, you still get 50% dmg boost which is multiplicative with total damage, not base damage.

Assuming you run elemental enhancement, asuma wb and iruka, you deal total of 100(base)+40(elemental)+30(iruka)+30(asuma)=200%tai/nin dmg. Barrier makes it 240%, but as that buff scales off of base dmg, real difference is 20% more dmg [(240/200)*100%], while yamato works like unparalelled, which increases your total damage by 50%. So if you only swap barrier ninjas for yamato, you deal 200%*1.5=300% (360% in case of water/earth because they benefit from barrier) instead. He's going to be best barrier ninja for every main, even better than hashirama. At this point you can safely auto (pompt barrier on move1) if you manage chakra correctly, so main uses mysteries while available.

The only thing i can tell you is that yamato appeared among the possible choices we could choose among in one of the last month feedbacks, but jiraya and orochimaru sannin war, the two breaktroughs implemented after that feedback, were not among those choices (they were yamato, kimimaro, tsunade sannin war, kabuto).