Official page at Epson.com is now up. http://www.epson.com/cgi-bin/Store/jsp/Pro/SeriesSureColorP800/Overview.do?ref=van_p800
Looking at the specs there is an image of the roll feed adaptor, and it appears to be more robust than typical of some of these printers (remember the 2200 roll feed?) It appears to be somewhat similar to what I have in the 11880 and easily could have some "geared assistance". The price also seems to indicate it's more than just a place to hold a roll of paper.
As far as nozzle density, based on output speeds which seem faster it may be 360 nozzles instead of 180 per channel. However, Epson has produced many printers with 180 nozzle density that had plenty of issues (the original 4800?) so here's hoping whatever made the 3880 so reliable made it's way into the new printer.
It does appear that for a 17" printer this will be the best choice for most. The 4900 offers some nice features, and of course the extra gamut with orange and green, but the new blacks and dMax may be more appealing and if it does match the 3800 in reliability then a sweet machine for sure.
As far as fading, I guess the printer can have a small affect on this because dither's and screens may change how much actual ink ends up on a print (set me straight on that mark), but I think the biggest factors are the ink itself and the paper it's on, so it should perform nearly the same as the p600. I'm excited to see Mark's results, Wilhelms results so far certainly looks promising.