Although Yamanaka was impressive against Jamoye he has, himself, stated that there are improvements to be made. Some of those are somewhat obvious, such as developing what he does with his lead hand rather than just lining up the straight left, whilst others seem to be less obvious and are more about making small improvements and tweaking what he does in the ring, such as controlling his balance a little more intelligently.
The fast turned in terms of how long Yamanaka was out of the gym is due to the fact he wants to record the 7th defence of his world title later this year against a notable opponent.
Yamanaka does seem to have mentioned a unification bout though unfortunately it's unlikely he'll get another of the Bantamweight champions in the ring with him and in fact all 3 of the other champions have mandatory title defences lined up. What seems more likely is that Yamanaka will be taking on a top contender, such as WBC #1 ranked Suriyan Sor Rungvisai (36-5-1, 16) or the #2 ranked Zhanat Zhakiyanov (22-1, 15), as he tries to prove he really is the best in the division.
No date or opponent has yet been set though we've heard a fight in Autumn is very likely and there was a rumour, a few weeks back, that it could be in Singapore on the same card as Ryota Murata's (4-0, 4) next bout. That rumour seems unlikely to come true but would make for a spectacular show if it does happen.
(Image courtesy of http://suljosblog.com)