V4 will be used in Poser until a viable successor takes her place. However that new figure will have to be able to use her content as well. If a new figure comes along and cannot use peoples huge investments they have for V4, there is no chance it will take off and the adoption rate will be very slow. In Studio, V4 is practically dead because the users there prefer the Genesis platforms and have the ability to port all off her content (skins, morphs, clothes, hair etc) over to use with that. What does this mean? Their Genesis figure is now also V4 and better. They have their V4 replacement, Poser users are still waiting for theirs. Because V4 was unchallenged for so long, asking people to throw away years of content collections is a tall order to ask just to try something new. There has to be some form of backward compatibility to ease the transition onto this new figure. If not, well V4's reign in Poser shall continue as the no.1 used figure.

Quoted for Truth. (And, to note that this is a Poser discussion, not a Poser vs DS discussion, as some might want to have it.) Also, V4 is a good figure. With fixes, which are all over the place, and the addition of weightmapping, if desired, it's an excellent figure to work with, with certain caveats that people have long solved. (Within reason for any figure this old.)

The question ultimately comes down to marketability and V4 IS the most marketable figure-content for Poser users. It surpasses the default figures by orders of magnitude and G series content just doesn't work well in Poser. In order to supplant V4, a Poser-Purposed next-gen figure would have to be created and it would need to be able to use many/all of V4 assets.

Honestly, there's not much wrong with V4's mesh/sculpt. A good re-rig for users of modern Poser platforms might go over very well and it would allow most character packages/morphs to still be used, too.