Ok, if you want a full reasoning here you go:
S-Tier: Has leaks and/or sayings, and/or hints from Sakurai, have their merits, popularity, and are unique and diverse enough to be considered.
A-Tier: Have their merits and hinted with recent events (such as Takamaru appearing in many games lately), big popularity, and are unique and diverse enough to be considered, but no clear evidence to be S-tier.
B-Tier: Have at least some of: their merits, have uniqueness and diversity, and decent or higher level of popularity to be considered in the final roster.
C-Tier: Plausible semi-clone territory, have merits, but for the purpose of when time runs out.
C--Tier: Has a shot, has a decent or level of popularity, unique at the very least, but based on their current standing, merits, and position they will probably not be considered for playable character.
D-Tier: Up there but too much of an obscurity or unlikely to be considered for various reasons.
But yeah, I might redo this later.