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If you mean 2 users for :apple:TV, there's some rumor that that may be a new feature of the next incarnation of tvOS... and may be announced at WWDC. However, if it is announced, it's probably not available to the public until the fall.

If you mean you have 2+ accounts on iTunes and would like to flip back & forth between them, I think that can be done by logging out of one and logging into the other. If you mean having access to BOTH iTunes accounts collections at the same time, I don't think that is possible.
 
Nope, unless the new gen one allows it, but I just tried to do this recently and I failed...
 
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