I think it's questionable that Sixaxis would have appeared in a 2005 console. The lack of any indication of that, and the short notice developers had to include motion support prior to E3, suggests it was still a WIP at that point. I'd also question removal of the HDD as that's a big part of the whole PS3 platform and a differentiating factor. I think Sony could have got away with maybe $50 on top of XB360's price to include a standard HDD, when you consider the profitability that could be obtained from downloaded content, but I'm not sure they could have launched at the same time. Also if they launched in 2005, there'd be none of the current online and Linux methods, as they're all in development. It'd just be a box to play games, and online games wouldn't have a very good online service. And the games back then would be pretty rough-looking too I imagine. Consider MotorStorm from 2005 versus now!So you take most of the great stuff about the PS3 (Cell; high performant PC GPU and solid tools from NV and OpenGL to facillitate PC interest and porting; Sixaxis; freem online gaming)
I think the delay has had the flip-side benefit of a strong 'first impression'. Launch titles look good. Services sound strong. There's a truck-load of features in the box, and things that really differentiate the console. A PS3 in 2005 would just have been another console without any fancy features versus XB360, and only the name to differentiate it if most titles are cross-platform.