If Lucas still holds original negatives/prints/whatever of the original films, nobody really knows for sure. Just like people say that they went to great lengths to destroy all prints of the original films that were released. One could probably make a case that either one of those statements is false, or that both of them are true. The truth is, we don't know what still exists in the "Lucasfilm archives" or in the hands of Lucas himself.
He could have 4k scans of the original films sitting around collecting dust for all we know. I remember hearing a report back in 2001-2002 that they had already begun digitally transfering the original film negatives. But again, who knows if that is true.
All I know for sure is that most of the people here are going to be dissapointed with the OUT release, no matter if they're interlaced and single layer or not. Five years from now when the SE's have all come out in the theater in 3D, we'll be having this same conversation about why the originals haven't been released on a modern format.