Well, I never thought I'd be asking this particular question, but, at this point, is it at all scientifically plausible to argue that _Deinonychus_ did not have 'feathers"?
Certainly. Even were it to be established beyond any shadow of a doubt that Deinonychus nests inside a clade with a feathered common ancestor (and by "feathered" here I mean having actual feathers, not the possible feather analogues in Sinosauropteryx) - and as some consider the oviraptorids, including Caudipteryx, to be closer to modern birds than Deinonychus is, I would say that this has not been so established - there is always the possibility that secondary feather loss occurred in the course of its evolution. As far as I can see the only way to render it absolutely scientifically implausible (as opposed to, say, merely unlikely) that Deinonychus lacked feathers would be to find a Deinonychus fossil showing that it had them.