Let's be blunt. You can do that. You won't be able to use it, but you can do it. Poser is hard coded to read poses from pose, figure from figure, prop from prop. It does parse files differently based on where they come from. Now, having P5, you do have the option of creating several runtimes. I generally grouped mine into "departments" like a stage set up (wardrobe, actors, makeup, set design, etc). But you can easily group yours into "V3", "M3", "Alexa" "laRoo", "Koshini", etc. within each of my runtimes, I've organized my libraries according figure, then within the figure subfolders I have different folders as well (MAT poses are in one folder, and it has folders sorted by clothing, for example). It means work, of course, and effort everytime you install a lot of stuff (I'm lazy and tend to do my installs in batches of 25 to 50 items at once, lol). But the effort is upfront, and when you go into create an image, it's all there.

thou and I, my friend, can, in the most flunkey world, make, each of us, one non-flunkey, one hero, if we like: that will be two heroes to begin with. (Carlyle)