I'm almost positive that smaller PDF publishers who stick to 3.5 after the release of 4E will do well for themselves. My prediction is that a sizable minority of the people playing 3.5 will wish to continue playing 3.5, and in a market that completely lacks official WotC support for these materials, people will flock to the publishers who continue to do 3.5 well. It may take some time for a new leader to emerge from the pack as the big players migrate to 4E, but I'm almost positive that it will happen, and whichever publisher(s) does the best job will suddenly find themselves a much stronger company than before.
I could be totally off base, it certainly wouldn't be the first time, but I really think that consumer skepticism will come into play in a major way this time around. A lot of people simply don't want to have to go through a major rules change every four years (on average).