This may be a bit like a snake eating its own tail, but try and follow along.  About two years ago I wrote a short piece about the lost levels of Super Mario Advance 4 (you remember; it's about those e-Reader levels that were never released).  Then yesterday I mentioned that article again when I commented on the rarest e-Card of them all (you remember; it's that E3 2002 promotional Kirby card).  LBD "Nytetrayn" mentioned that article on his Poison Mushroom site, but in doing so he recalled the old lost levels article (you remember; it's the... no, wait, sorry, already recapped that one) and went on to say this:

It is my conviction that not only should Nintendo make the fourth and final Super Mario Advance a part of the Player's Choice line, but they should do so in the most compelling way possible: by including the missing levels, items, enemies, features, and so forth in the cartridge. I realize that this would obviously take more work than any other Player's Choice version of a game released to date, but there is precedent for such things to occur; Devil May Cry 3 from Sony's Greatest Hits line, for just one example.

Now that's a great idea.  That is a lot of work for a new Game Boy Advance title at this point though.  I know I'd buy such a thing if Nintendo went through with it, but at this point I'd expect that unused material to turn up on the Virtual Console somewhere down the line instead.  Someone add it to the wish list along with Mother 3 and Star Fox 2.