The LFE (subwoofer) channel from Hairy_Hen's 5.1 upmixes use the LFE from the '97 LD 5.1 and the '04 DVD 5.1, depending on which sounded better for each scene, adjusted for volume to pack a little extra punch I believe. You'd have to ask Hairy_Hen directly, though.
I think it'd be an interesting experiment, but I'm not sure what you'd do about things like Mos Eisley or Lapti Nek. Splice in an upmix, I suppose ...