I personally believe that Mega Kangaskhan is extremely broken, and every team needs to run a counter just for this. As a result, it is my belief that...
IT SHOULD STAY IN OU.
Yes, really. Let me explain.
The reason being that it uses up your Mega Evolution slot, and by banning it, you overcentralize the metagame again. Think about it. Before Gengarite was banned, everyone used their Mega Evolution slot on Gengar, with a few using it on other pokes. Gengar was the best Mega (besides Mewtwo/Blaziken, which are ban-worthy even without Mega Evolution).
Then Gengarite was banned, so everyone who did have Mega Gengar on their team switched to using other Megas, most notably Mega Kangaskhan. The gameplay of the tier has shifted. Rather than trying to counter Mega Gengar, everyone just shifted to countering Mega Kangaskhan instead. Because that is what became necessary.
If Kangaskhanite is banned, then who's to say that these same people won't switch over to Mega Lucario (great attacking stats and Adaptability) or Mega Mawile (105 Huge Power!) or Mega Medicham (a better movepool and is faster than Mega Mawile, albeit less bulky)? Heck, even Mega Heracross probably gets enough use to the point that it's (probably) not going to be in UU. And we just ban Mega Stone after Mega Stone until there's nothing left. Mega Evolution, which is supposed to be the gimmick that separates Gen VI from Gen V, will be regulated to Ubers-only play before too long.
I worry that if we go ban happy on Mega Stones, we open up this very real possibility. And thus, this new gameplay mechanic will go largely unexplored (as a majority of users prefer to play OU over Ubers). And since this is something that Smogon has no history of dealing with, I feel that we should think about this before jumping to any conclusions.
Is Mega Kangaskhan broken, even for a Mega? Maybe. But until we do more extensive testing on Mega Evolutions, I don't think that we can say that for sure, so I don't think that the Kangaskhanite should be banned right now. Maybe after a suspect test, I will be proven wrong. At that point, I will no longer object to the ban.