Indeed, some features were much more complicated than anticipated, mostly the dungeons (and the dungeons' editor) and the vehicles.
These two features we started in January are gameplay challenges but also and above all technical challenges, because they are closely related to our blocks engine. We got tons of technical issues to overcome that eventually induced a mountain of work.
So, we will go on Steam after the summer, when we are ready. The goal being to bring the most polished product possible on Steam.
But, in a few days, we will be delivering another alpha version. This is not the Steam version yet, some content and improvements are still missing, but you will be able to test the new features.
In order to be able to give you the best possible gameplay, your feedback will be most welcome as always since the beginning of the project.