If anyone is still interested in hacking this I am happy to share my info on this. I have info on the e-reader level format (which is vastly different from the format of the SMB3 ported levels), as well as decompcression code for the levels stored in the .SAV file. I'll need to dig stuff, but just informing that I do have notes available though I warn that it's messy =)
I'm still interested in this, I have a habit of getting distracted so not much accomplished ;sweat;
Yeah, I'd like to see what you got!