User blog comment:~Silverstream/What Will Happen to Jemma Simmons?/@comment-26831386-20150814133557

Its a gateway to attilan. The reason why Jiaying thought it was dangerous was because everyone who went through didnt come back out, but its actually a doorway to attilan that can detect the inhuman gene within people and pulls them in to send them to attilan. I doubt simmons will get powers, more likely she'll spend a good portion of the season in attilan where her "destroy anything alien" attitude she developed in season two will be a plotpoint as she learns a lesson that what's alien to her is familiar to others, and you cant just destroy alien things because they are alien to you.