Here's what the great Bulbapedia had to say:
While the standard encounter rate for a Shiny Pokémon (either in the wild or by breeding) is 1/8192, the Masuda method multiplies this rate by 5 (to 5/8192 or about 1/1638) in Generation IV and by 6 (to 3/4096 or about 1/1365) in Generation V.
Basically this is saying that the Masuda Method's chances are 1/1365 in Gen V. Since Gen VI doubles the chances of this I'd say that you're looking at 2/1365.
Take into consideration that this is just a guess. Nobody really has clear data on Gen VI Masuda Method yet, we're just basing it off of Gen V data and the fact that the rate is doubled.
Hope this helps!!