It's all about politics. If you're the most powerful ruler you make people come to you.Doesn't mean he still can't have the horn. But I feel like it would have been teased in some form or another by now if he did. Otherwise, it becomes a weak Deus ex machina to pull it out of nowhere and control a dragon in the midst of battle.
PS, not sure how many of you have read the princess and the queen, that details the dance of dragons. But qyborn didnt invent the large crossbow to defeat dragons. And dragons are hardly invincible in GRRM's world.
What gets me is why wait for John to come to dragonsstone? Between his ride to white harbor and then sailing south to dragonstone. It could take a couple weeks. Danarys could fly to Winterfell in an afternoon. She has the westerosi hyper loop at her disposal. She needs to take more advantage of it. That's how Aegon was able to conquer the seven kingdoms.
As for Euron, he had THE most bad ass entry in GoT history. Dude rode in on a giant bridge (shaped like a mouth or claw) that crushed a dude and then preceded to kick everyones ass.This season, he's supposed to make the bastard of Bolton look tame. I cannot imagine how that could actually be.
My only question is, I saw one of the sand snakes get the back of his leg. What are the odds he was poisoned?