The beta development for 1.12 wrapped up in May, and it is now the default version. Some of the initial design decisions of 1.12 had to be changed in the light of existing player saves, but it in the end it held well overall, and it's a very major improvement in the simulation quality of the game.
Private 1.13 development has already started. Two major new features have already been implemented: walk legs and station halls. These correspond or solve some very often suggested features by players. To read more on how they look like read the devblog for this month:
https://carloscarrasco.com/nimby-rails-may-2024/