I understand, most are skeptical about Snyder delivering a good Superman movie, including myself. (Though I really enjoyed Watchmen and even Sucker Punch purely for its visuals).
But I don't necessarily consider that Snyder was being disrespectful in regards to the Reeve costume. The pros and cons of the costume was also debated in length in the
costume thread. And though I wish they had gone with a more traditional choice of bright colors, Reeve's costume is a product of art of its time.
But as long as I live, I know there is no other incarnation of Superman that will replace the image of Christopher Reeve being Superman for me. For me and many other fans, Superman IS Christopher Reeve. Sometimes even when I read Superman comics, though the art may not resemble Reeve, in the back of my mind I am still imagining and associating the Superman character with Reeve.
He is the one who made that suit work and it worked great 30 years ago. But it certainly may not work for another actor for a modern interpretation. Of course there are many who might wear the Reeve costume and might look good for costuming at conventions. But it may not really translate well on screen for a new movie. The costume will look dated and his comment about it being from a costume shop doesn't really sound absurd nor disrespectful, cause the person wearing it can't carry and pull off that vintage appeal of the costume. It could be argued that then it should be a different actor, but I don't think any other actor will make that classic costume believable like Christopher Reeve did for a movie.