Golfweek's bifurcated list (Classic & Modern) started in 1997. We used to have 10-14 new courses a year make each new subsequent top-100 Modern list. That was in an era when course openings numbered 250-350 annually.
In the past three years, new course openings are down to 125-150 a year, and the number of new courses making our list each season for the first time is down to 4-5. There will be much less turnover in the future, so that the pace of decline in the standing of new courses that make our list is also likely to slow down. In other words, I don't think there's a strong enough argument for a third, Post Modern list.
Besides, we've now created a separate grouping of Top-40 Best New Courses to cover those that have opened in the previous two calendar years. So we're already highlighting those innovative layouts without having to showcase them on the top-100. In other words, we have plenty of lists already.