Now THIS is a good topic. The predictions you've come up with could end up being shockingly close, or way off the mark, but I do believe that the world will change quite a bit due to 3D printing, and also Artificial Intelligence. This is something I've been thinking about a lot lately too, so this was a great read!! I've actually been designing my own 3D printed miniatures game that takes place in the future, and the backstory for the game will itself include 3D printing! Right now there are 3D printing technologies that can make much stronger titanium than the current SLS method, because the process actually raises the metal powder above the melting point, instead of below it as with SLS. Also, the cost of the powder is apparently going to be able to drop because of recent methods for making titanium powder that is closer to the ore itself, meaning much cheaper to produce because less modification is needed.

I'm thinking that possibly by the year 2080, 3D printing and AI technologies could be to the point that an army of AI ULV (Unmanned Land Vehicles) could be created in a matter of days/hours instead of months/years to produce and train conventional military forces. Perhaps we could even have remote-controlled vehicles on other planets/moons/asteroids also, where it is too dangerous to have humans living, but instead we could control unmanned vehicles from orbit in a space station or other ship. This gets around the delay issues of controlling a mars probe from earth for instance. If you instead control it from orbit around mars, it would be a similar delay as a satellite above earth, right? So much closer to live control. Perhaps this could be a viable way to mine asteroids and moons/planets?

3D printing technology is already getting faster too, so given decades of progress, there could likely be exponential increases in the speed of the process. At that point, it IS practical and justified to pay more in material/energy/maintenance to 3D print for mass production, IF you can afford the extra costs. If it were only 5 times faster it could be worth it, and by 2080 it could be even more.

Oh, and one more idea, in response to the idea that "3D printing filament price will always be directly tied to oil costs" is not necessarily true, is it? PLA is becoming pretty widely used, and it is a resin made from corn, right? Plus, it doesn't emit the awful fumes that melted ABS plastic does. Also, there is the possibility of recycling plastic containers to make filament, cutting costs. So the filament price doesn't necessarily have be directly tied to oil prices.