Well, the 100k listing fee is notional, but (I'm sorry to say) your negative reaction is to a certain degree something I expected.
Part of what I struggled with was the relationship between such an auction house and the current market areas. I understand that many people advocate completely dropping the current markets and and replacing them with a more traditional unified auction house-style interface. This may or may not happen, and I thought I would offer forth a proposal on how an auction house might be introduced that could co-exist with the markets, and add functionality that they do not provide.
I believe that while the markets provide MOST of the functionality of a unified auction house, there is at least this niche that is missing -- true bidding, global view for rare/unusual items. This view casts the auction house as a premium institution, while the market areas are the common method of selling.
If the listing fees are very low, I believe that this would create a parallel and competing structure with the market areas. Quantities of low cost material would tend to flood on to the auction house, instead of being sold in the market areas. While this may be to the liking of those who advocate replacing the markets, it was not my goal in this discussion here.
My rationale for choosing 100k as the listing fee? A somewhat arbitrary benchmark that items that may sell for 1M gil and up would be the target for the auction house. At a sell price of 1M gil, the fees are 200k, netting 800k for the seller. This high cost would, ideally, be justified because the seller would ultimately get a higher price and/or sell much faster than attempting to sell the same item via the market area. With a rare item, it can be difficult to determine a reasonable price -- too low, and you've lost opportunity, too high, and the item doesn't move. This bidding-style auction house give a clean in-game mechanism to quickly assess the market and converge to the highest price that someone would pay for the item.
At the same time, I tried to set a price that is high enough to make selling of common items via auction house unprofitable. Puk wings, logs, ores -- all of these things simply do not sell for enough, and so the market area remain viable for the majority of materials and items. When a person accesses the auction house, they would expect to see very high quality items being offered, not millions of "junk" items.
However, I understand the concern that this makes the proposed system unusable for lower ranked players / crafters, or people of otherwise modest means. This is why I (in the second post) proposed an alternative listing fee method, that allows for lower fees (and hence lower cost items to be listed), but based upon the availability of the items within the market areas (short version - listing fee of 5k per item available in the markets, max 100k).
I think that ultimately there is an inherently fuzzy separation between the markets and this proposed version of an auction house. Any attempt to strictly enforce a separation would likely feel overly forced and stifling.
Thank you very much for posting your feedback. I won't claim to have thought of every repercussion for this, so more the more pokes and prods the better!