They may have sold that low but only because manufacturers ramped up production thinking the crypto bubble would keep going. Then the market crashed, the used market got flooded with dirt-cheap retired mining cards and AMD/AIBs were stuck with a large commit of no longer sellable parts they had to get rid of at severely discounted prices. Not only were the 8GB RX580s retailing as low as $120 but that also included a promo for your pick of one free game out of three offered, so knock another $40-70 if you were going to buy any of the three games for anywhere close to retail.
Probably can't do that due to GDDR5 being discontinued by most memory manufacturers. If AMD is going to re-spin a chip just to accommodate the fact that GDDR5 is no longer an option, "Big Navi 204" with all of its worst handicaps resolved would make more sense. Give it encoders/decoders, 4.0x8 at a minimum and 6GB/96b memory.