I doubt there's a market, but there are people still using the earlier figures. I find it easier to get a good variety of 'actors' by using different figures, as long as I can work with their limitations. Nearly all V4 characters still have that family resemblance when you put them side-by-side...
The cast list on one of my current projects includes weight mapped V3, the G2 males and females, and even Victoria 1. Antonia is on standby.
I can make or refit most things, but I'll still snap up a useful item when I see one if it will make life easier. That doesn't constitute a market, by any means.