Nintendo 3DS

Considering the significantly better rendering capabilities of the 3ds when compared to the DS, I'd say you won't see a ton of FMVs to begin with. You can fit a lot of stuff into 2 Gigabytes worth of cartridge space when you don't have to store 8 or more texture passes at high resolutions for every surface. Burnout Paradise, which is a gorgeous racer and even open-word, takes up less than 3 Gigabytes iirc.
Also, since cartridges have significantly shorter access times and faster reading speeds then say, the PSP's notoriously slow UMD drive, there isn't a lot of need to cover up loading times with FMVs either and you can use much more aggressive compression technologies too. Resident Evil 2, which was released on 2 CDs originally, fit onto a single 512 Megabit N64 cartridge (that's like 64 Megabytes)
Regarding flash memory: it's certainly not that expensive anymore and is going to get cheaper and cheaper as time progresses, but it's also very, very slow, especially at large sizes.
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"If god didn't want us to eat in church, he would have made gluttony a sin." - Homer Simpson

From: sigistauffen | #081
but it's also very, very slow, especially at large sizes.

I think this is what SgtThom is trying to about larger Cart sizes.