Well, I know that some thermoplastics can be mixed with good results. I've a roll of polycarbonate-ABS in my printer right now. Normally polycarbonate prints at 310C, and this blend prints at 295C.
Ive seen other blends as well, with intermediate temps between the 2 initial plastics. Now, I only have experience with PLA, ABS, Nylon, PVA, Polycarb-ABS, and HIPS. A lot of this is still unexplored as it took industrial quantities to do anything.
WHat these machines will allow is experimentation on small batches and how plastics work and don't work. And that's awesome.