I really like this idea! I'm currently working on a sort-of TDK styled Batman Beyond build, and it's funny cause I seriously thought about using a Captain America costume as a base; total coincidence by the way, I have never seen that photoshopped picture before (which is pretty cool by the way). I decided against this though because of the ridiculous price and I had no way of getting my hands on one to feel the quality of the material before purchasing it.
Just my two cents, I considered using a wetsuit as a base too, but I heard from alot of people that wetsuits can get very warm and uncomfortable at times, even if vented areas are cut out of it.
So, I decided on a pair of men's work coveralls. The ones I got are made of a durable cotton twill that is sort of like canvas, and they don't actually heat me up all that much. I plan to get them tailored to fit closer to my body and look more like a superhero suit, and then I'll dye them black.
So yeah, I'd recommend that route if you haven't already started with a wetsuit yet. Your choice though. Here's a link to the ones I got:
Red Kap® Zip-Front Cotton Coveralls - jcpenney