BC & AD are overwhelmingly popular despite most of the world not being Christian.

Pretty much all of the religions support it, and we will therefore see a lot of resistance to this change because it will feel like an attack on religion to them.

Of course one day, perhaps a century or two from now, everyone on earth will use bitcoin every day and think in blocktimes. At that point it'll just happen on it's own, no organization needed.

You're just too early to be giving this much thought. Much like I was when I posted this exact topic on the BitcoinTalk forums in 2012. ;)