Demand will still outweigh supply, but usually Apple racks up 3-4M in pre-orders the first weekend a new iPhone goes on sale. Assuming the device doesn't go on sale til end of month (at the earliest), Apple will have ~ 600K in supply. We should also assume that supply will only increase and not decrease over the coming weeks, as they refine the manufacturing process.
Let's not forget with the 'new' 8 and 8 Plus, most consumers will still go for these devices. While us forum goers can more easily justify spending 1K on an iPhone, most consumers find $650 already very expensive, and likely won't go for this more expensive device. Estimating 3-4M of pre-orders, divided by all 3 devices equally (which is still unlikely to assume 1/3 of consumers will spend 1K on an iPhone), we're looking at a demand of 1-1.5M for the new Phone for pre-order weekend. That still outstrips 600K in supply, but it's not quite as bleak as this rumor is making it out to be.