There have been several articles on a liquid metal robot based on a single paper. This is that paper. It's about using microwaves on an easily meltable metal and how it can be reformed using magnets. That's not the T-1000, but it could help with 3D printing by making a base for the shape and then melt away.
Plasma thrusters are more powerful than they seem. A team was able to get a small thruster to emit the same power as a larger one.
My personal prediction is we'll have universal construction factories in Earth orbit. These would be open to anyone to make requests to over the Internet with some standardized logistics protocol, where you upload designs or select existing products. Most of the raw materials would be mined by robots in space and the delivery networks would be completely on auto-pilot. Eventually you'll get robot factories making more robot factories and miners, which exponentially expands production capacity and drops costs of goods. Products are bundled on regularly flying dropships to the surface, then picked up by companies for delivery. It's the closest we'll get to eliminating scarcity like in Star Trek, although that's not actually possible because capitalism/economics is an absolute law.
You could of course do all this easier on Earth, and 3D printers are kind of an evolutionary prototype, but there are a few logistical areas that make the technology more likely to coincide with the industrialization of space.
Also helium 3 is in abundance on the moon and asteroids. I see lunar mining operations and eventually Martian colony