I thought dolphin did that...
No it didn't, it did exactly what the WiiU does, provide backwards compatibility, nothing is rendered in HD. It's only done in the HD release of Okami, GoW etc. which are individually developed.
It was a mammoth task on the 360 but the original PS3 managed it easily enough with half a PS2 inside it.
Anyone who thinks its anything but a mammoth task to provide re-rendered emulation of a library of games is utterly fucking deluded.