Rohan was born in a war zone. Within his first year of life, he was displaced from his home, held captive by a hoard of crazed terrorists on two separate occasions, and was an eyewitness to a giant killer spirit rampaging through his hometown.
Rohan is three years old and already 10,000% done with everything
Heres something I noticed when referring back to the trailer after watching the episode. If these spirit vines are able to regenerate easily(like in the scene in 3x01 after Korra tries to spirit bend them away), then imagine how much spirit energy/power they could gain from them. Kuvira is going to need something to help run her army and those giant mecha tanks.
In the clip from the trailer, we see Varrick’s hair blowing but what is more important is the background. There are multiple smaller pieces of spirit vine in their own tubes. I think these individual tubes will be used to run the mecha tanks. In the screen shot from The Coronation, there are wires hooked up to the vines, like they are going to drain the energy.You can see the bolts on the capsules are similar. If I was going to put a tube that holds my power source, I would probably put it in the back of the suit also.
I also want to mention the fact that there was some HUGE foreshadowing to this in the season finale of Book 2. Varrick is in prison, but what exactly sets him free? THE SPIRIT VINES.
Also Bryke mentioned that there was something that links books 2, 3, and 4 together. I think this is what they were talking about.