The main evidence against Coldhands = Benjen is the Child of the Forest saying he died long ago and that why would a very, very long lived being like a CotF claim a guy who died approx. two years before died "long ago?" Personally, I think there's been way too much focus on that line, but I dunno if Coldhands is Benjen or not. Could see it happening; could it not as well.
Either way, I don't think they'd cast Benjen's actor as Coldhands if they bring CH into the show. His very enigmatic nature means they'd have to cast someone else to play the concealed character even if they plan on revealing him as Benjen later.