I'm betting the new bags will be still be pricey for most if not all of BfA, since those mats will be also be in demand for lots of other current crafting like endgame gear. In fact the 30-slotter will probably cost much more to make than
Hexenzwirntasche, although AH prices could end up around the same.
And if the 32-slot bag ends up selling for even only 1 or 2k more, there'll still be lots of players not willing to shell out that much more for a couple of slots. Never underestimate peoples' willingness to go cheap for a modest upgrade instead of getting the best available. A few years ago during the first few months of WoD, when
Hexenzwirntasche were new and more expensive due to rarity, I was still selling tons of Embersilk and Abyssal bags (22 slots) for only a few hundred gold less than Hexweave. I was making much more profit overall than the
Hexenzwirntasche sellers because I was using old mats which were much cheaper at the time. Many players were obviously in the market for bigger bags but not willing to pay for the new hotness.
