Hah, we’re afraid it doesn’t work that way. Di2 stands for Digital Integrated Intelligence. Of course Shimano could add another I to that and call it Digital Integrated Intelligence Improved (Di3)… but it’s more likely that they will just increase the existing model / product codes.
Having said that though, Shimano are rumored to announce and release Dura-Ace 9200 sometime in 2020. We’ll keep an eye on any announcements and post news as soon as we hear anything.