My son just turned 6 and he now wants to stay here until he is 13 so he can become 'swiss'... so cute and such a turn around from wanting to go home as soon as we got here.
I would strongly recommend that he gets citizenship before he goes. He doesn't have to do anything with it. But when he does come back to see you in 5 years or so it will make life just one bit easier.
And it might help with the 'ladies'... fancy accent, flashy passport... etc. Australians love the Swiss, even though some don't know where the country is...