If you look at the site statistics (https://www.fimfiction.net/statistics), you will notice two things about the number and type of stories over time:
1) The ratio of Everyone and Teen stories to Mature has been decreasing for years;
2) The number of new Mature stories has been extremely stable for years.
If we extrapolate this out, it means that in a few more years, the majority of stories posted to FimFiction will be mature; and most of those are porn/clop, from my observations.