It's not. People wanting to do that should wait for at least Ouya. Modern MAME runs "the classics" up to Space Harrier well enough on a T30 Tegra 3 (e.g. Nexus 7/Ouya) but definitely not on an ARM11. The fact that the people pushing the KS claim MAME runs fine on the Pi tells me everything I need to know about how legit the project is.