There's some discussion in this thread:

https://www.renderosity.com/forums/threads/2977561/march-23rd-right-around-the-corner

I'm a little disappointed, since they promised us unimesh and a new figure. End users probably won't really notice, though. Hopefully this means no unimesh yet, not that they've given up on it. As I understand it, unimesh support/figures will make Poser more compatible with other software, making it easier to import and export stuff.

Note, unimesh as DAZ used the term a couple of decades ago is not what they're talking about here. No unimesh support doesn't mean you can't use V4. It's a completely different definition of unimesh.