the most important thing is what conditions will be when buffon retires... maybe chiello will have a great decline and lose his starter spot (or even leave). that same can happen with marchisio... i expect buffon to play another 3-4 years so alot can happen in that time...
I'll never forget his twitter fight between him and several other Juve fans including fake melo and adam digby's come back was - "At least i got a season ticket in Curva Sud"
the important thing is he will ber starter at the time buffon retires (pirlo will be gonne by that time too) so there will be no competition for who the next captain is. maybe, just maybe chiellini has a chance but i believe marchisio takes this one...