I may be way off base here having not actually worked for an RPG company but I will throw this out there anyway.
How much of the development of materials is really based on the crunch in the PHB? For example, I am currently taking a group through Paizo's Rise of the Runelords. The most interesting elements of the story are crunch-neutral. You could tell a very similar story in other systems - and it would be similarly entertaining. If this is the case, why can't publishers (of modules anyway - and its seems that is pretty much what is left of 3rd party development anyway) simply write the stories and leave the crunch for later when they actually get the SRD?
For example, if I were writing an adventure in anticipation of 4E, I would develop characters and settings and leave placeholders like ***swashbuckling fighter type*** or ***blaster mage***. This would be a larger problem (with less predictability in the types of characters available) at higher levels but the initial interest will largely be at the low level anyway.
So, you could have two or three modules ready to roll except for the mechanics of creatures. Once the SRD comes out, you could go back and add in the crunch and even make some revisions based on interesting new options (new characters or monster types, new environments, or new abilities) but most of the work will have been done already. All you need to do is slot in some predictable encounters.
Consider this. With a raise of hands... Who really thinks there won't be orcs, skeletons, zombies, giant vermin, and other predictable creatures for low-level encounters? The bulk of early modules will draw from these sources anyway.
There are some dangers in this approach, certainly. One would have to rely on the last three editions vision of what is available to low level characters. This may fail to spotlight the new features of fourth edition (like the rumored new core races and classes) or - worse yet - rely on materials not available at launch (like the yet to be identified, gnome like surprise exclusions). This does not strike me as a huge risk though. When the SRD does come out, one can substitute new material in to places where you already had encounters - now with new 4E flavor.
The larger problem is playtesting. I see this as a real concern and one that I simply don't know much about. I don't know how much play testing goes into the typical module - especially one at launch. There would not be much time for this if one has only a month or so between getting the SRD and release.
So, I see some problems with playtesting but not much in terms of module writing. I suspect I could convert the Paizo's Burnt Offering, for example, in a weekend. It has
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lots of goblins, meaner goblins, bigger meaner goblins, classes PC race enemies, and a few support creatures.
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This would be easy to adapt to 4E.
Flame on....