While you bring up some potential food for thought, I find the prospect of 3D printers and their proliferation as a means that threatens the adult collectors market to be totally ridiculous. We are all aware that many toy companies, manufacturers and businesses are beginning to use 3D printers more often, creating designs with ever more complexity. But even if 3D printers were to become more commonplace in the future, they would just be 3D printers etc.... 3D printers can mold shapes and pieces of a figure, but the pieces that are produced still need to be assembled. Not only that the pieces also need to be painted with expert detail and precision.
There is a reason why the majority of figure collectors out there choose to buy "finished" pre-painted figures rather than model kits. That being most of us suck at doing model kits and painting anything that actually looks good. That and its time consuming. You could sort of say the same about sewing machines. Sewing machines are rather commonplace and have been for much of the latter half of the 20th Century to the present. Yet I don't see too many people going out to the fabric store to buy raw materials and make their own clothing at home to wear or for work. Simply put we all ain't that skilled or simply don't have the time to do it.
If there ever comes a time where 3D printers have an automatic "paint" function that provides automization similar to printing out paper documents from your laser/ink jet printer....then I'd be worried. Until then I think those that truly believe that 3D printers can make toy manufacturers obsolete can dream on....
Anyways to give a better idea of what current 3D printers can do when applied to toy design and manufacturing I use the example of Figma Mirai, an action figure designed and made by a japanese action figure company that specializes in bringing popular anime characters to action figure form. This particular figure was designed in 2010. It saw release in summer of 2011. Below are pictures of the initial prototype printed out from the designs done using a software program on the PC computer. An advanced top of the line 3D printer was used to manufacture the parts.
As you can see the figure still needs to be assembled and when thats been done the figure is very very rough. The plastic likely very cheap and the figure itself is very unpolished.
Now compare this 3D printed prototype with the finished product released a year later....
Even if I had a 3D printer that could mold an action figure in pieces for me, painting it to the standard presented in the mass production version is not a very pleasing prospect. I dont have the tools...ie: the paint, airbrush or skill to finish this figure properly. I'd much rather buy the figure in its mass produced form than try and make it myself. If anything 3D printers will allow those with the modding abilities to make every more complex works of art. I'd like to see more of that happen. But at this time I just don't see 3D printers being a threat to toy manufacturers that make action figures or even vinyl figures.