I always believed that keeping the spirit portals open so the humans and spirits will have to co-exist was a foolish idea and the last season demonstrated why I was correct in my assessment. It allowed one of the most dangerous organizations to return from the brink of death, paved the way for humans to discover a new energy source they used to create a WMD, and fostered a conflict between spirits and humans that hasn't existed in literally centuries.
There was no reconciliation. One scene that is a testament to Korra's mistake of allowing the portals to exist is when Korra asked the spirits for help, the spirits reject. The sole intention Korra had for allowing the spirit portals to exist was to foster a camaraderie between humans and spirits that would have them work together to defend the new world they live in.
It didn't happen. The spirits bailed on Korra, despite the fact that the WMD was powered by spirit vines, a product of the spirits. Now humans and spirits despise each other just line Wan's time and seriously hamper the quality of life of the other just by inhabiting the same space. It's only a matter of time before the spirits and humans wage war on each other.
And it's all Korra's fault because she blindly allowed her feelings to control her actions without considering the consequences, neglecting to see how different cultures of two completely different species would usually end up fighting each other due to their differences.