In general, a surprise revelation would be awesome if it fit.
[In reply to]
But for The Hobbit, I see Legolas' 'job' as identifying the people of Mirkwood and exploring their role in things (be that the capture of the dwarves, BO5A or even a role in the expunging of the Necromancer at DG). For that reason, just including him quietly in something seems like a good idea for this story which already has so many main characters and dimensions to it. I don't mind if he has this "moment of conscience" mentioned with regards to his fathers decisions - just as long as it somehow fits in with the people and their story - and doesn't become too much all about him only.
*Not that I'd mind a story about Legolas* - it's just that this is not really about Legolas (but I think he has a part in it). And fortunately/unfortunately (depending on how you look at it) he has the awesome starpower to really draw attention to him or to something else and could easily take over scenes and plots that really ... for this story ... shouldn't be about him at the center this time around - in other words it wouldn't take much to accidentally make it about him. In some ways, a surprise revelation kind of points to a story about him ... but it depends on how it is done - how long the camera lingers with him (especially if it's just him) afterwards - how exceptional he becomes compared to all the other elves (although - he is exceptional compared to the other elves in his father's realm since he is a sindar elf like his father) ... etc. ... how much the things he does fits in with either Thranduil and his decisions and/or Gandalf and the White Council and other elves at Dol Guldur. I hope that he fits into one or both - maybe he has to decide between them - that's fine - but hopefully he decides quickly and it means something to the story and not just to his story.