I doubt they would hold products back intentionally. They might turn down V4 vendered items, since v4 isn't their focus, but it would be bad business practice to purchase an item only to keep it locked up. Of course, it's also bad business practice to take away basic site functionality, and they did that with the website, so, you never know:) 

My guess is that some artists are creating content for both genesis and V4 on the hopes of appealing to both Poser and Studio users. Personally, I don't even check any more. So, if there are items there for V4 and company, I wouldn't have noticed, because I don't even click on support items for figures (clothing, etc) when I do happen over to DAZ's site.