I still don't know why you think this is an actual argument. It's not. The Future Warrior body armor suits have yet to be proven either, and that's definitely what TDK takes it's cues from. Furthermore, there's plenty of stuff about Batman in these films that we take for granted but are in no way proven or even currently possible.
Take, for instance, the grappling gun. Sure there are grappling guns, but they are essentially RPG launchers with a big case full of rope that has to be carried around and a far more extensive harness and winch system than the Batsuit uses in these movies. Yet we buy it. The electro cape/glider set up is probably the least realistic thing about this Batman and we still accept it. Why does the body armor need to be what's actually proven? If Wayne Enterprises can develop and make functional things that are not possible right now and Batman can then use them, why would spider silk or liquid armor be out of the realm of not only possibility, but plausibility. The whole point of what Nolan's been doing is taking things that are real or in development and advancing them quite a bit beyond where they currently are and saying "here's Batman."
Just because you are more stringent in your body armor evaluation does not mean the general audience will be. They are going to be far more open to explanations for spider silk or liquid armor or dragon scale armor than you seem to realize. Hells bells, they'd do another Batman Tech thing on the Science Channel and tell us all about how those things are real and in development and possible in the not too distant future... and then they'd put it in the special features on the Blu-Ray and digital releases.
It's that simple.
Alternately, they could say he's wearing a layer of extra strong, but flexible, advance kevlar body armor under the heavy fabric of his body suit. And folks would buy it.