Well, I've been looking at the level header data and I started to figure it out. In particular, I've mostly figured out how pipes work. I've also figured out that there is a mechanism to stop the sceen from flipping on some screens. With these things and a few others figured out, I've decifered almost all of the level data. There are still a couple of bytes who's function is unknown, but it's pretty well all accounted for.
I've discovered a bug in my level renderer. The elevators/platforms are rendered four pixels lower than they are supposed to be. I hope it's not too big of an inconvience to you to remember to correct for this when building the levels. Also, as the current renderer doesn't take the movement codes into accound, elevators/platforms are all currently rendered as though they where large size. I'm planning some more changes to the level renderer, but I can't say when they'll be finished and the next set of renders will be produced.
By the way, I played the world one beta and it's pretty cool. I didn't go over it with a fine toothed comb, but it seems to be pretty accurate. (Except for some background elements, like bushes being larger.)
Me and my roommate gave it a try and he managed to beat it on regular and hard mode. My roommate, did, however find something he didn't care for. In level 2-1, he managed to get stuck. He'd use the wall jumping trick (or whatever it's actually called) to get to the top of the level and then fell in the hole where the 1-up ends up after you get it. He couldn't get out and had to time out.
I don't really think this could be considered a bug, as it's not even possible on the original game, and depends on glitch abuse to even reach. Furthermore, the way the 1-up drops down like that depends on it, which is a kinda neat little thing, so it proabably should be left as is. I just mentioned it as it was some playtester feedback.