Unless you want it to be HUGE there's no way your gonna make it last that long.
If you use 9v alkaline, that's pretty much true. But if you use Li-ions or li-polys, and a Snes clone, 10 hours is perfectly attainable in a reasonable form factor.
And just to reiterate, 9v alkaline batteries are a major no-no. You would get very little playtime, and you would go broke replacing them.
Current trends place us at *incoherent male orgasm screaming* by late 2013