I agree, plus Bankai takes time to achieve, time that Soul Society doesn't have.Apparently none of you can think logically. Zaraki isn't getting a Bankai.
Before his training he was already a monster. After his training he's back at full strength and achieved his Shikai. That's all the power-ups he's gonna get.
-No mental restraints
-No eyepatch
-Both hands
-Shikai
Enough said.
What's the point of him getting a damn Bankai? The Quincys would just take it.
The whole purpose of Zaraki being Soul Society's secret weapon is because he doesn't need Bankai. That's why Kyoraku had him trained. That's why the Central 46 was afraid of him.