It is more about the Shrek films
https://mgba.io/2015/10/20/dumping-the-undumped/
They used custom cartridge types (somewhat similar in ideas to some of the older consoles) to break the size limit that everything else (including the videos most already know about ( http://gbatemp.net/threads/buying-a-gba-flash-cart-in-2013.341203/page-18#post-4756995 ) used.
I agree it is likely not a massive selling point like a SNES flash cart suddenly being able to use all those nice special chip games but if it was easy enough to do then I guess they added it and it is a claim they can make.
I don't know what goes for using the extra space in homebrew (and I doubt meteo or the others will be able to take advantage of it) at this point. I am hoping we do get it though -- the GBA does not have the best media players but you can do nice things with them, and various programs back in the GBA era did already exceed that size for limited types of flash cart (see pogoshell).
Rumble
Yeah few games support such a feature.
They did release a guide to allow you to hack it into more games and as far as hacks go it is not that bad of one.
https://gbatemp.net/threads/make-your-own-rumble-game-for-ez-flash-omega-definitive-edition.580909/
The DS stuff I am waiting to see what goes for. I doubt they will be adding more games to the list of things the EZ4 supports (if at all) as much as GBA slot DS homebrew (there are a few things that work better there) or just a DS mode launcher to have a touchscreen and whatever else to launch games, maybe also pull from the DS clock to set the internal one.
Goomba vs hardware. Emulation on limited hardware will always be limited compared to actual hardware. That said if someone played the GB/GBC library on it they will certainly have a sense of the GB/GBC and be able to say they played all the GB/GBC games.
