This is getting rather off-topic. I'll try to get it back on topic.
Anyway, it is true that the SNES/GBA changes are mostly ASM. While there are a few level design changes (most notably the addition of Dragon Coins in nearly every level (some of which are sprite Dragon Coins), and midpoints in nearly every level (many of which don't fit SNES SMW's midpoint system) except the Star and Special Worlds), I don't think many people would be interested in playing it for those-- if you're going to be using an emulator anyway, might as well play the actual SMA2.
The main use I can think of for a hack like this is for people to use as a base for SMA2-styled hacks, and for that, level design changes are irrelevant (and palette changes are nearly irrelevant since a lot of hackers seem to use custom palettes anyway).
By the way, that list missed a lot of changes-- for example,
- You can save at any time, including during a level
- Reloading from a save does not reset your score/lives/power-up/etc.
- You don't have to release all other buttons when screen scrolling, and you can use L+Up or L+Down to scroll the screen upwards or downwards
- Front Door and Back Door's timers were increased
- Timer bonuses are higher after Koopalings, Reznors, Big Boo, Bowser, and the ? orb in Sunken Ghost Ship
- The status bar still appears in the Bowser battle, meaning it's possible to gain points in it, as well as die from time up there
- You're warped to Yoshi's House after the credits, instead of the game just freezing on the ending screen
- Castles cannot be re-entered with L+R, but they're rebuilt after defeating Bowser (with new graphics that have flags on top) and can be re-entered then; the castle destruction messages are shortened (and the cutscenes are skippable) after defeating Bowser
- After completing the Special World, if you replay any Special World levels, the game keeps track of your high score in each level
- Fishbones can be killed with the cape (note that if you use Tweaker to make this possible in SNES SMW, they'll hurt you during their death animation, but they don't do that in SMA2)
- Chucks give 2000 points (instead of 1000) and drop 5 moving coins when killed by fireballs
That's only what I can think of right now.
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Advynia: a Yoshi's Island editor - Alyssa's Unlikely Trap demo 3