The novelty of unlocking characters isn't as welcomed nowadays, thanks to the internet. Considering youtube/etc has dissuaded Sakurai from another SSE (thank goodness), I hope secret characters become a thing of the past.
I think a huge thing to consider is how much Smash 4 is being used as cross promotion, and that leaving major hype reveals for post-release is probably not favorable marketing-wise. If Sakurai goes down the routes of unlockables, I am willing to bet most of the secret characters will be Brawl B-listers like Ike and Lucas, characters that have their fans but don't generate much discussion pre-release.
I think a huge thing to consider is how much Smash 4 is being used as cross promotion, and that leaving major hype reveals for post-release is probably not favorable marketing-wise. If Sakurai goes down the routes of unlockables, I am willing to bet most of the secret characters will be Brawl B-listers like Ike and Lucas, characters that have their fans but don't generate much discussion pre-release.