SSDs (or mainboards with more SSD space than 512gb) are the bottleneck right now. When you configure a new one delivery time gets bumped up by a solid week on BTO when you add more SSD space.
Yeah that is what is giving me pause. I can grab the model I want with s 512GB right now at my local Apple store, but iI need/want 1TB and that pushes it out to 9-16 September. And if I do the Trade-In, that has to go back by the end of the month so I could be without an iMac for two weeks or more, which is really a non-starter.
I'll keep an eye on BTO ship dates to see if they free up once this initial rush of orders is processed (the Barclay's promo period is good for purchases charged by 29 September). If not, then I soldier on with my 2017 for another year or so until the "Big Screen" Apple Silicon model is ready. And honestly, it's still 100% usable for my needs so it was only the 50% "discount" doing the trade-in that was making me think of upgrading.