We have done extensive research, and spoken to many artists about forums. Based on feedback from artists, we have decided that we will not be adding forums to ArtStation. We may change our mind in the future, but for now there are no plans to add forums. It just doesn't fit in with the product vision as a professional portfolio platform. The majority of artists we speak with want ArtStation to be focused on the art, and less about the drama and noise that forums bring.
Generally, forums are a relic of a early 2000's. Most people have moved on to Facebook. There are many great Facebook groups now for artists to share their work and get feedback. E.g. Level Up and Ten Thousand Hours. If you're looking for a place to share and banter, there are great Facebook groups that allow you to do that.