Have a player who's interested in this line of feats, but spending eight feats for SLAs seems like an overly hefty price for the current benefits. even if some of the SLAs are nice. Especially when the character isn't a primary caster (mysterious stranger gunslinger) and therefore won't be able to pump save DCs.
I personally houseruled that a kitsune has a number of tails equal to the highest spell level they can cast. So a kitsune that can cast 9th level spells has 9 tails. It gives no mechanical benefit, but it's flavor my players really appreciate.