Thankfully, he hasn’t been resting on his laurels. Although his trips up to the Tokyo have been infrequent, especially since the ROBO-ONE competition format changed, he has continued to be a dynamic supporter of the regional RoboCountry IV competition in Shikoku, and is actively engaged in introducing young students to the joys of robot development.
At the same time, Yamaguchi-san has evolved the Onimaru robot design through three generations and is hard at work on Onimaru IV. Hopefully we’ll be able to spend some together in March during ROBO-ONE 17. If not, then we’ll just have to hop a plane down in his direction. 
Here’s a brief introduction to Onimaru 3’s capabilities including a really slick handstand:
The only question in our minds is, “How can Yamaguchi-san improve on that?” It’s hard to imagine, and will be wonderful to see. We can hardly wait!