Default Will android L supported our device

Just curious, I ve read in nexus thread they will support some of their device. Even my old nexus 7 will be official supported by Google. I also read Google I/o that with the new feature of chromcast we can do mirroring and one of the supported device is our lg. But to do so we have to received new menu called cast out if I m not mistaken. And that menu will only appear in android L. Doesn t it make sense.
Sorry mod if this thread a little out of the topic.
Thanks

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