Well you have a bit of point there Wes...
The Youtube author hangs a great deal of his argument on Childs' parka going from dark blue to tan---
I've just watched the scenes in question: Childs is wearing a dark blue/green parka when MacReady tells him they're going to to get Blair. In that scene there is (from left to right) a navy blue parka, an OD green parka, a lighter green parka and a tan parka hung up on the walls.
However in the long tracking shot (in which the "Thing's theme is heard for the second time in the film) when we get to the same spot Childs was standing at, there is- a tan parka, two OD green parkas and two more tan parkas.
To me this just seems like a continuity error. :unsure
Gettting to Childs' appearance at the end (where the author claims he is wearing a tan parka), it seems more like his dark green/blue parka is just frost covered; his pants (which where definitely a dark blue) appear the same way as his jacket- frosted giving the impression they are lighter in colour.
Now I don't know what the hell to believe. :unsure :lol
One thing (no pun intented

) I'm sure of is that during that tracking shot we are definitely looking through the Thing's eyes. However it could be Blair-Thing just as easily as Childs now being a Thing.
At any rate, Childs behaviour IS unlike how he has behaved throughout the film- it doesn't make sense that Childs would go out after "Blair" alone in the night. Childs is not the "hero" type to leave the safety of the camp on what could be a suicide mission.
Another thing about the exchange between Childs and MacReady at the end- as Mac hands Childs the bottle of whiskey Mac has his eyes completely trained on Childs with a slight smirk on his face- it's as if the bottle is one more "Thing test" up Mac's sleeve.
The second Childs drinks from the bottle the "Thing's Theme" plays again for the third and final time (and becomes the end credits music). Mac chuckles as Childs enjoys the drink.
What the hell does this mean?!? :wacko :angry
Is the music cue an indication that Childs is a Thing and "failed" Mac's test?
Or is Mac's chuckle a sign that he believes Childs is still human? Does he believe the Thing wouldn't "enjoy" a drink of whiskey? Was Mac expecting a reaction similar to the computer frying at the start of the film?
Or maybe...
Just maybe...
Mac WAS a Thing at the end!
Mac handing the bottle to Childs (and him accepting it) has sealed Childs' fate...
And Mac's "chuckle" is more along the lines of-
"ha... I got you."
(Well personally I don't really believe Mac was a Thing, but that's the beauty of this film; it has you guessing right to the end!)
PS- I really wish I could illustrate all this with screencaps, however I don't know how to do this with a bluray disc. :unsure
Kevin