According to the WBA the two teams have 30 days to make an agreement on the fight, however it appears that they may have that deal done sooner than expected with Taguchi's promoter already stating that an agreement was almost made between the two camps for a fight in August, which we already know would be Taguchi's next defense.
For Taguchi the bout will act as his fourth defence and sees him facing a genuine world class fighter for the first time since he won the title, back at the end of 2014. He has improved since that title win but hasn't been facing the stiffest of competition and it's time to see if he can actually beat a top Light Flyweight.
For Miyazaki the bout gives him a chance to become a 2-weight world champion and to bring the WBA Light Flyweight title back to the Ioka gym, where it had previously been by Kazuto Ioka. Whilst he is the mandatory challenger he appears to be there by relative luck. Mioyazaki is on a 4 fight winning run, since losing to Fahlan Sakreerin Jr in late 2013, but those wins have come against very abject opponents.
The bout, from what we understand, will be announced shortly and will be for August.