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Personally, I would not play the demo, because I tend to get attached to the pokemon I use in battle. I would not want to experience Kalos for the first time with select pokemon, only to lose them.
As there are only 12 days to go before the games are released, chances of the demo being released now are slim. It's not long before almost everyone is playing the final copies now. If you have any other eShop related questions, please ask them here.