You just reiterated why I think SSJ3 is a fluke transformation. It can't be achieved under any normal circumstances. And even in the extremely unconventional scenarios where SSJ3 is achieved, it still has immense drawbacks and it cannot be fully controlled.Lord Frieza wrote:I don't think SS3 is a fluke. It just a form that under normal circumstances saiyan wont achieve it.
Goku only achieve the form while in otherworld when his bodies did not have the same limitations and Gotenks was a fusion. It might be impossible for a saiyan to naturally attain the form.
As for Rage well if their is a saiyan who knows what true rage is, its Trunks. His life has been hell and every-time he thinks things are getting better they take an even deeper nose dive. The basic SS forms are fueled by strong emotion, to even unlock the form you must be driven into the depths of rage, frustration or sorrow.
Rage it would seem, ties back into that theme. While the Goku and Vegeta have unlocked the more serene god powers, Trunks has has been pushed harder and deeper into his rage then anyone else, and like Gohan and Goku before him, found an even greater power hidden within him.
But I also like your theory behind SSR. I mean, it established that intense emotions can lead to incredible spikes in power and can even be the bridge from one Super Saiyan form to another, as shown with Gohan. My guess is that all the rage, anger and frustration that's been brewing inside of Future Trunks from all the many years of mentally and emotionally exhausting conflicts finally reached the boiling point when Future Trunks was made to feel guilt from Goku Black and Zamasu's scathing speech about how his selfishness of using a time machine to interfere with even in the past to save everyone in his world was in itself responsible for instigating all the events that caused misery for him, his friend, family and billions all over the world. Unable to cope with that mental burden, Super Saiyan Rage was born.