I don't see anything in the tech specs to say for sure, but I would guess that it's the same as the 2011 models, basically that it works as an external display but only for computers with Thunderbolt.
I think they would have specified a mini-display port if it were the case. Therefore, I believe that it can only be a second screen for another Mac via the Thunderbolt interface.
Yeah that doesn't even answer what we are asking, do the new iMacs support the display in feature using thunderbolt. The old iMacs did in like 2010 in 2011 they stopped it I believe.