Honestly, part of my thoughts with the 9070 and its higher price is not just that its an upsell; part of me thinks they're actually not getting that many dies hitting that yield, so to make them they're actually cutting down fully working 9070XT dies in many cases, and thus they'd rather you just bought the 9070XT, unless you for example need the (actually fairly decent) reduction in power and heat the 9070 non-XT likely brings. I mean, the 9070 is dropping clocks by 15%, core count by about 5%, but power is roughly 30% lower, so it's definately a more efficient part, and realistically in many cases, failed dies are LESS efficient/optimal, not more.
In this sense, its not so much as an upsell, but a premium on a less cost effective part, with the 9070XT NOT being failed dies, but actually just dies that are being cut slightly, and downclocked to put them lower on the optimal heat/power curve; thus the premium; it's a cut full die, rather than a defective one.
Without an eye inside AMD though, its hard to know if thats the truth, or if it is just an upsell; but honestly I could believe it, as they'd have had an even bigger mindshare win if they'd announced a 499/599 RRP for the two cards.