Why are S2 sets grey and missing in the addon? It also says "NYI Blizz". Same deal with S3 and S4. S2 is definitely in game, because I'm standing near the vendor. Then why the likes of S2 neck don't have costs? It feels like the addon is abandoned.

They got implemented a couple of days ago (#179), but its currently only on the development branch.
@Hoizame is mainly active on the weekends. The updated Build probably comes next week.

All 4 Season sets are added with next version