The two remaining routes have been in development simultaneously with the Early Access build. As it currently stands, Kuna'a's route is finished writing and I'm currently writing Aisa's route---since writing is what takes the longest by a Long Mile, the two routes will probably be released much sooner than two years. I anticipate early next year based on where everything is at right now!
The first 4 routes were completed in about 3 years, and that was while balancing my PhD and releasing another game, both of which I am not doing right now LOL. In a recent devlog I talked about how much content I was able to create for the Early Access build without these obligations, so I wouldn't use prior development timelines as an indicator of my typical game development progress!