There are a lot of approaches to additive manufacturing. Fundamentally, however, they all break down into a few categories:
Planes means using sheets of material. This approach is usually more of a combination of additive and subtractive, since the excess sheet has to be trimmed away. Lines means using long thin noodles (floppy or rigid) to build up the part. Points means using powder, either laid down in a bed or shot out of a nozzle.
I’ve been trying to come up with a way to take Fused Filament Fabrication (FFF, AKA: the copyright free version of FDM) to the next level by removing the need for a support structure. If you can free up the extruder nozzle to move in more dimensions relative to the build surface you can print “overhangs” right onto the part instead of printing them onto thin air.
This approach would definitely allow an extruder-style printer to print nearly-arbitrary shapes faster and with less waste. However, it would not allow printing of truly arbitrary shapes. The easiest example of this limitation is the spiral. It doesn’t matter where you start from, an extruder-style printer is going to have to use support material to print a spiral.
Ultimately, if you want to print arbitrary shapes, you’re going to have to hold everything in place until you can get the entire print finished so that every little bit is attached to every other little bit. Either you use support material, or there are some things you just don’t print. That being the case, might as well embrace support material, and nothing is supportier than a powder bed.
CandyFab is a good open-source example. Here’s a great overview of the process by How It’s Made (my favorite show evaaar!)
There is a sort of natural difference here between hobby 3D printers and professional 3D printers. Powder beds allow for truly arbitrary shapes, but they require a lot more of the printer and the environment the printer is in. I think this means that hobby 3D printers will be limited to nearly-arbitrary shapes. Maybe in a decade there will be pro-sumer printers next to the drill presses at home improvement stores that will use powder beds. It’s at least a possibility.
The result of my investigation, and the point of this post, is that I don’t think the open-source hardware movement is going to drive the development of powder bed printers. I think those are going to be left for the professionals.