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I have read that the new $1 coins will have the same "signature" as the Sacagawea coins, so any vending machine that accepts the Sacagawea coins should accept the new coins without modification.

And the Sacagawea coins have the same electromagnetic signature as the previous Susan B. Anthony dollar coin, so vending machines have been unaffected for quite a while.

From http://www.usmint.gov/kids/coinNews/circulating/dollarCoin.cfm
The Golden Dollar shows Sacagawea, the young Shoshone woman who traveled with and helped Lewis and Clark to explore the Louisiana Territory. The golden color is not gold, but a mixture of metals, specially chosen to not only look golden to human eyes, but to look the same as the Susan B. Anthony dollar to vending machines. The new dollar has the same "electromagnetic signature" as the old one. That means the makers of the machines don't have to change the machines so they can "see" the new dollar.
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