Yes, the 2004 release was done in 1080. It was scanned in 1080, new footage was integrated and it was color corrected in-house at Lucasfilm, then sent to Lowry for clean up.

I don't think Lucas will ever re-do it. Why would he? The prequels were done in 1080 as well (except Episode I). If ROTS had its effects done in 2k then they are higher resolution than the actual film. And either case, who gives a flying fuck, Lucas can dick around with his special editions until he dies for all I care. Re-doing it in 2k is almost pointless because there isn't much difference; 8K is becoming the new standard, but I guarantee you no Special Edition will ever be in 8K.

Also, why would going to the negs be counter-intuitive? Today you wouldn't re-conform the physical negative, you would do a DI, just like the 2004 special edition doesn't actually exist physically on the negative. If Lucasfilm ever got serious about the original film it would be easy to make a restoration from the negs.