Robins tier placement will be mostly based on match ups. That said, I think what direction the meta game shapes into in neutral will be what decides it. Robin has tools for most situations, if the game shifts into floaty air control Robin is really threatening with Levin sword and projectiles. If it's a ground game Robin has projectiles, good range and threatening tilts, but lacks grab range and movement speed (I've been told the run speed is similar to Links, don't know about walk speed as that's important ad well).
Robin to me doesn't seem like a character that has anything game-defining in his kit, so it all comes down to his tool and abilities in the match ups of what characters become strong. It's not uncommon for otherwise meh characters to get by in mid/high tiers because they have specific tools that work well in the meta, or against specific, good characters (#1 example is jiggs in melee, she's a pretty bad character that has the tools to win match ups against great characters like shiek, falcon and peach and go even with marth/falco, while struggles vs characters like doc or young link because they thrive in the sort of game play her kit forces)
Robin has great adaptability from what I've seen of him, so it will all depend on what characters become good and popular, and what Robin can do about them
(Specifically watch out for duck hunt dog, ZSS, little mac and shulk imo)