Not to veer too far off-topic, but I think the number of tails is linked to Champ's level. As they rise in power, their tails increase. I believe it's Level-1, so at max level 10, you'd have 9 tails. As more expansions open up and the level cap increases it will become more noticeable.
This is of course not accounting for the scripted scene with Tail-Chopper the Butcher boss in the Tychris expansion which causes a loss of (one) Champ's tail. (Don't worry, you can regrow it with the right TF item again.) For a kitsune, unfortunately, there is no such item, yet, implemented for growing multi/additional tails... so technically only 8.
But I hear that in the Tychris expansion... they also plan to implement a TF item for that...
Trust me, or they don't call me 'Honest Ace'.