I'm pretty sure they'll just get this shiny new thing so that instagram users would have a text-based platform as well - as they can only share images there. The walled garden would come from the fact that you can still see people's images only on Instagram - I understand this will be a text-only app. And what will #Barcelona not have will surely be:
- The ability to freely change platforms (i.e. move from #Barcelona to #Mastodon along with your follows and followers, like you can do even on Mastodon currently).
- The ability to change to a different server completely, if you dislike the moderation or stuff (I recall @atomicpoet once said with his previous Mastodon account that it will be Federated, a few months ago, not sure if I understood correctly, but I don't think they would want to lose some users and their data to servers they do not control)
- Not to mention the ability to format your posts, like on other #fediverse platforms like #Friendica, #Calckey, #Misskey etc.