I always liked comparing Sunny to Starlight being they both have radically different thinking from the world. (I kind of wish Starlight still had some of those activist traits but for good even in post reformation)
As for Sunny, I think not just in the movie but as character traits, I think she the potential to be one of the funnest and most complex characters in MLP.
I think they should explore how Sunny’s strong idealism can be both a good thing and even a bad thing.
I think she would be the type who thinks with her heart not her mind. She might not see the nuances and complexity of a situation. And at worse she might even be bossy and authoritarian to make sure what thinks would be right could be done.
But of course in addition, I also want to see Sunny as a proactive character for good. Perhaps she would be the one to initiate a party or she would be the one to have Pipp and Zipp bond even if they don’t want to.
And most importantly in keeping with friendship, her flaws can be balanced out by her friends who she would needs just as much as they would need her. Especially Hitch who would be the perhaps to one to help Sunny think more rationally and perhaps bring her back down to earth when she might be going too far in a certain way. And Sunny would teach him to think big and to not be afraid to do great things even if it isn’t the normal way.
I think Sunny has so much potential to be both a great heroine who has both great strengths and great flaws. And great friends to help her on her quest.