I didn't see them as rantings, really, but something that Miles knew that we have yet to find out. I find the "breed an army of Mistings" idea that Wax hits upon a little unwieldy. Let's look at the 4 (6 if you count the two they didn't get) women that were kidnapped by the Vanishers. Assume each woman is made to give birth as many times as possible. Most women seem to be taken at an older age than you would ideally start breeding for this kind of project at. At most you are going to get 100-125 children. Assume all are Mistings... 125 Mistings isn't a huge number. Particularly when you add in Gnats, Smokers and Seekers. It's honestly an awful awful plan.
So what is the Set doing with these women? Well, I have to look at their one common thread: Spook. And what is the one thing Spook had that no one else in the Mistborn series did? Sazed's book. What if the bloodlines they are hunting down contain clues, somewhere, to the knowledge of Hemalurgy? If so, an army of Mistings becomes much more feasible... and dangerous. Instead of risking getting some fairly useless Allomancers, you can get powerful Allomantic abilities into your well trained army. I'm more inclined to think this may be the case because of Marsh's involvement. A plan to breed Mistings is honestly a bit small potatoes for Marsh... but the possibility of Hemalurgy being reborn is a very real threat to the world.
