The two men are familiar to each other with Taguchi being responsible for Inoue's only distance bout. That bout, Inoue's 3rd as a professional, saw the "Monster" being taken the 10 round distance by Taguchi, who lost his Japanese national title to Inoue in a hard decision contest.
Although complete details on the sparring haven't been released, and neither has footage, we've been informed that Taguchi stated that he felt both fighters had improved since their bout last August. From watching Inoue in action, especially in his title winning bout against Adrian Hernandez, it seems clear he has, though we've not managed to see either of Taguchi's recent bouts.
At the moment neither man has a bout arranged but sharing the ring together would suggest they are both gearing up their training ahead of announcements for their next bouts. Hopefully those announcements will come shortly.
(Image courtesy of http://www.watanabegym.com/)