For me, "Why leave V4?" isn't quite the right question. For me, it's at least three different questions.

Why support a new figure? Because vendors won't keep making things for V4 (or M4). If you like buying new stuff, and you want that new stuff to work in Poser, you should support a modern Poser figure. Otherwise, vendors will eventually stop supporting Poser altogether. It's about time to you know what or get off the pot. We all, including Poser's creators, have lots of choices. I've seen Poser used at the university I used to work at, in all kinds of works randomly online, in the oddly popular anime RWBY (and then talked about by its fans like it's high tech), and even once in a hospital. In every single one of the cases I've seen outside of this community, it was used for creating content, with only the default content used. In none of those cases did its users buy content.

If the Poser content community supports a new figure, just as we did with the highly expensive, poorly UV mapped, limited morphing V1, it will benefit the Poser content community at least as much as it does the creator, if not more. V4 is what she is today because she got years of community support. In the form of millions of dollars and hundreds of thousands of man hours. As someone who felt she was different but not better than V3, and said so when she came out, I'd say she got that support from the beginning. I remember how many vehemently told me the community would fix all the problems I listed immediately (we only fixed her shoulders, and that took years), and how very few had similar criticism. Trust me, you remember when you get dogpiled. V4 got widespread brokerage support immediately, with only a very few vendors supporting older female figures in releases after hers.

No single group, let alone a single person, is going to be able to do the same, no matter how much time they have. If we wait for that to happen, those groups will have to move on from the Poser market long before they're able to duplicate all that work.

If we want future Poser content, we have to support a modern Poser figure. DAZ won't do squat for Poser users anymore. That ship sailed when they made DS, and some people are just now noticing it pulling out of the harbor. It's past time to move on.

Oh, and I also just really like some of the more recent advances, like topological improvements and weight mapping.

Why keep using Poser? In my own opinion, because DS is annoyingly limited, very closed, and poorly documented. Can you sculpt in it like in Poser? No. Sure it's got GoZ, but so does Poser. That's like saying Poser has AutoFit because it has GoZ (instead of more accurately saying it has it because it has the Fitting Room). I could fix the mesh problems I had with V6 in DS in seconds in Poser. I find it hugely frustrating to work without a sculpting tool in my posing software. Can you make your own dynamic clothes, or convert other people's clothes? No. DS users have to use an arcane process just to use MD clothes there, and from how it's been described to me, it's got some significant flaws. You have to treat poses as morphs, which (from what I've been told) has the same problem using morphs instead of rigging does. I can use MD clothes in Poser, and even convert some conformers. And I can do what I do most- make my own clothes in Blender and use them in Poser. For me, that's a whole lot I can't do in DS. Can I make add softbody or cloth dynamics to mesh hair? No. You look at, for instance ken1171, who uses soft body physics on his figures and hair all the time. If wolf359's work is the standard for professional, his animation is more than adequate for professionals. My aspirations aren't so high in that area. I hope to use soft body physics on hair in the future, and if I can get it to work half as well, I'll be ecstatic. Can you build your own materials, like you can in Poser? Well, technically yes, but there's no documentation about any of the nodes (or "bricks"). I mean zero. Can you just load DS source meshes into other programs the way you can in Poser? No, because DS uses a custom, proprietary format for its source meshes. As far as I can tell, they're no more efficient than .obz files, but a whole lot less easy to mess with. Which means it's harder for me to make morphs that work properly in DS. In Poser, it's been dead easy- load mesh from Runtime (maybe after unzipping) and sculpt. In DS, I have to use an exporter, which adds a layer of error to work with. Can you edit DS files in an editor? Only if you mean a text editor. There's no equivalent to the free or commercial apps out there to edit Poser files. And DS files are full of extraneous information that clutters the file. Information you might not want in files you publish. But the community seems to poo-poo the idea of an editor, so I don't see it happening any time soon.

Which is just one of many examples where people flame and rant about an issue in Poser, yet make light of it in DS.

Sure, I'd love for Poser to be even better than it is. But as a content creator, even if I stopped selling Poser content (which I could see happening- brokerages aren't going to accept V4 content forever, and they're already pushing G3 support hard), I wouldn't stop using Poser and use DS instead. I like being able to make what I need and hack what I have. And not only is that sometimes impossible in DS, so far as I've tried and witnessed, it's always crazy difficult. From my perspective, DS is easier when you don't mind the work it forces you to do and/or don't mind working inside of very particular boundaries. DS is the only app I have ever used with gaping holes in its documentation, where even its experts don't know how things actually work. Which frankly, makes sense. DS is a loss leader meant to sell content. Poser is a posing tool for content creators that includes content as a loss leader and an example the way Photoshop includes stock art. Of course DS makes creating harder for ordinary folk. It will probably make things harder and harder as DAZ customers become more and more of a captive audience. I'm sure it's a lot easier for PA's in the DAZ inner circle who get advance copies of DS and access to people who can tell you how stuff really works. But that ain't me, nor is it most people.

Why keep using V4? Well, for the same reason you might as well use V3 (much more realistic facial features) or V2 (TenTen, anyone?). Because when you pair modern features like the Morph Tool, subdiv, and bullet physics with older features like cloth dynamics, and render them with modern materials, you can get great results out of unique and high quality content that you already own. I have a ton of content for V4, but I think I have even more for V3 and A3. Sadly, not as many morphs. And I do really appreciate the weight mapped versions of V4.

And here's the thing. If we just replace V4, we'll have exactly the same problem we have now if that one figure creator decides they want to stop supporting Poser. The Victoria line is still full of innovations discovered and shared by the community. If you even look at 3D in general when V1 came out, Victoria wasn't special until we made her so. Most V1 and V2 morphs were custom. It wasn't until V3 that "characters" were just dial spins. JCM and ERC were community inventions. All that time, work, energy, and money will have gone to waste if we don't transfer what we learned to other figures. And it certainly doesn't make sense to make the same singular and risky investment a second time.

Over all, I think we need to get back to our roots. When I came to this community, new projects were greeted with cheers. People tried new things, and others encouraged them. Sure we cheered when people did stuff for new figures, but we were just as enthusiastic when people did things for older or less popular figures. People didn't bitch about Maya Doll, or tell BatLab or Yamato not to bother with her. We didn't try to silence people who liked Terai Yuki. I only saw people marvel when some forum member (I forget who) made the V2 teen into an amazingly real middle aged woman (one of the few Poser or DS figures I've ever seen who had proper hips). IIRC, that was during V3's reign. We championed projects that expanded what was possible in Poser. And we didn't spend so much energy discouraging others just because they wanted to do something different.