|Garde Manger Guy|
Although the lack of an official "we will most likely never do another hardcover revision again" statement so far is interesting, I doubt that it will happen. Even though I personally would love to see second darkness redone, doing such a thing comes in conflict with the way paizo is currently running their operation.
If they did announce that they were making a SD hardcover, you can bet that they wouldn't be able to give away the last of the original stock of SD material. They are still trying to sell it at every sale event, so it stands to reason that there may be a copy or two still left in the warehouse. However if you could prove that an updated product is something that people would be willing to buy, you may stand a better chance at getting it done for all the early products. Specifically in this case, the conversion of all 3.5 works to PF.
How? By creating a seventh part of the SD AP. Include all of the official conversions, class changes and advice on plot rewrites that the author feels is needed. Release this product in PDF form only to minimize the time/treasure/talent drain on the Paizo staff. Note however that this cost may still be too high to bring the product to completion.
If this seventh part is profitable(key word there) with a AP that didn't sell particularly well (IMHO there), it could prove to the company that more conversions could in fact be profitable to do. With this plan, you also gain the ability to sell those extra copies of SD sitting in the warehouse as it is not a full conversion.
In a perfect world, every AP could have a hardcover book full of shiny, glossy, full eratta-ie goodness two years after release. The economic reality is that you have to be able to prove that what you are proposing is viable and profitable for the company.