This is what I suspect will happen:
Company ACME has a 3e-type product called ADVENTURERS that is successful. They want to continue to publish expansions to ADVENTURERS, and they also want to do a 4e-type version.
The owners of ACME form a new company, called EMCA. ACME licenses ADVENTURERS to EMCA. EMCA stays with 3e, and publishes expansions to ADVENTURERS.
ACME creates a new product, which is similar to ADVENTURERS but not the same. It takes advantage of the new 4e system to go in a different direction, though at heart it has most of the feel of ADVENTURERS and is written by some of the same people and is marketed as "From the makers of ADVENTURERS". ACME calls this new product EXPLORERS.
From there on out, ACME goes with 4e, and continues to only publish products for 4e, while EMCA handles all 3e products, and continues to only publish products for 3e. The two companies do not call their products the same thing, or make them too similar, but similar enough to offer much of the same feel and the goodwill that comes with having some of the same writers and owners behind both companies.
I do not see why this would not work, given what we know right now. It is a bit of a pain, because you have to use two companies instead of one, and two administrative costs instead of one, and two marketing and promotional routes instead of one, and two settings instead of one, etc.. But ultimately, I think it could work. It might even get some people to buy both the 3e and 4e "versions" of the products since they are not identical and will have some significant differences. It might appeal to people who like the general feel and the quality of the writing but who might have two different gaming groups, or groups that might want to switch off between games depending on the type they are interested in playing at that time, or people who want to pillage new stuff from one game to use in their other game.