That's hard to determine, but it's quite apparent this gen that if it were a choice between MS's XB360 with 512 MBs RAM sold at cost price, and Sony's XB360 with 2 GBs RAM sold at $100 loss, Sony's consoles visuals would look a hell of a lot better! Something as simple as a significant RAM improvement is all it'd take. Or lets say next gen is one conosle on 100GB/s RAM bus, and the other on 500GB/s, the latter is likely to have significant advantages that become apparent in games.
As other have said, will devs use it? First parties would, making it a choice the fits better with Sony's structure than MS's, although MS can always commission titles. But otherwise will it be a case of hardware for no reason, like XB versus PS2? Quite possibly. But then the point of the loss leading isn't really to provide the better experience as much to get the sales. Even if the better console doesn't have better games than the rival, when people going into the shop see the two boxes for the same price and read the numbers on one box are much bigger, that's going to help sway them. XB wouldn't have got anywhere if it wasn't a loss-leader, because it'd have been priced too high. And if it didn't trump PS2 on specs, what would it have had to compete with PS2? "Same specs, same price, far smaller library and none of your mates has one - get an XBox!" vs. "twice the memory, three times the power, the most powerful gaming platform ever created - get an XBox!"
Yeah, it's not as simple as that. Maybe there's a case to say cut back on the hardware and invest in the marketing instead. It's not an easy choice to make though, to release a knowingly 'inferior' product and hope to fight in other areas. MS at this point can focus on Kinect, but there's a good chance the rivals will match. I'm not seeing room for a Wii-type console this gen. Sony should have sorted out PSN by then. Nintendo will likely have crap online no better than PSN now, so they'll be on the back foot there, but they'll be riding their brand high. In terms of services, content, etc. it all looks like being much of a rub, and only the design, specs and marketing are going to differentiate.
(This is why one company wants to abandon the traditional format and launch a tablet based console with docking bay
)