I'm just saying, imagine a mix of the UYIs without the polished guitar sound, without the reverb taking the life out of Matt's drums, with Axl's voice crystal clear in the mix on every song (instead of being buried in the mix on some songs). Imagine the UYIs with the mix of TSI. Loud, raw guitars equally mixed, drums lively and organic. Part of the reason Appetite works so well is because the mix is so organic and it gives every member of the band breathing room, and they shine. The performances on the UYIs are just as strong, but Slash's lead and rhythm parts blur into one sludge on many songs, Matt's drums sound flat and lifeless; Axl's vocals sound buried.
I've heard some unmixed versions of some of the songs - at least, before the final mix and overdubs - and they sounded great! Youtube "Axl's Advanced Copy" and you'll find rawer versions of the UYI songs before the final mix and overdubbing process.
There's probably more than a few of these type of demos floating around....so they wouldn't even need to re-record anything....remixing/remastering it would be enough.