The O-neg is no longer the 1977 or 1981 version of the film, it would be configured as it was for the 1997 SE since those altered pieces were put into the O-neg. Thats what Lucas means when he says the "original film no longer exists"--it doesn't in a sense, you would have to take apart the O-neg and re-edit it back to the way it was before the 1997 SE. The pieces that were trimmed or removed I am assuming are back in storage somewhere. Personally I'm not quite sure I'd want the OOT from the O-neg anyway, since I'm sure they would mess up the color timing, though the IP's have probably faded to the point where color correction is necessary anyway--personally I'd love to have that dye-transfer technicolor print that they used for color reference for the 1997 SE.
And yeah, Lowry got the O-neg scanned, thats why it looks so pin-sharp; were it not for the low resolution of the scan it could have looked better than it did in theaters.

As for resolution, 35mm is generally considered to be transferred more or less accurately at 4K, though I believe there are now 8k scanners that would ensure a truely lossless transfer. The 1997 SE changes were only done at 2k because thats all that technology had back then. Its a shame that the prequels were in HD; and not only HD but 2000/2002 HD. Right now I am working on a film that is using the same cameras and lenses that were used in AOTC and the HD tech we have has done nothing but complain about how crappy they look--in our case, we are just doing a TV movie so it is acceptable, but its really sad that the prequels were made with these things. IMO the only camera that I would ever consider using for theatrical release is the Genesis, or perhaps the Arri D20, its the only thing that will hold up on the big screen (but even then it still has that HD look).