wow that sounds badass how long have you been working on it?
I started on Friday night! That screenshot showcases roughly five combined hours of hacking. I'd probably spent about twice that getting that far, but that includes hacking in new music (which, yes, works on both bsnes and real hardware - I've witnessed it on both) and a failed attempt at putting Tap-Tap The Red Nose into the area underneath Yoshi's Island 1.
I now have map names displaying. They default to "Map XXX" where XXX is the 3-digit hex number of the current map. I've also hacked HP down to two digits, and I've moved the coin counter up. The second line of the status bar is going to be reserved for indications of what you've collected so far.
The end goal of this is to turn the game into one large contiguous level, Metroid-style. Mario's HP will be expandable via one-time pickups, he'll have unlockable abilities (currently at least planning Ground Pound, Wall Jump, Triple Jump and maybe a sliding attack; normal spin jump will be locked at start as well), and he'll be able to collect healing items either by purchasing them or by picking them up when randomly dropped by enemies. I'd like to add new powerup abilities too (hammer suit, frog suit, tanuki suit and maybe boomerang suit, each with world-expanding powers) but I don't know how easy that will be. Similarly, I'd like to add new enemies, including bosses, which I know has been done before but seems to have a bit of a learning curve to it.