The problem is cost. The best process is sintering using either a laser or electron beam. Additive systems using a welding head are nowhere near accurate and very dirty in terms of smoke and soot. Sintering has its own can of worms including a cheap source of powdered or granular metals.
To sinter with a laser you need a laser and a box to put it inside of filled with an inert gas like nitrogen or argon. Nitrogen is cheap but people would have to buy or rent gas cylinders and keep up on getting new filled cylinders from a gas or welding supply company. Not exactly user friendly.
Now for the laser: A 500 watts cheap, compact, continuous wave laser would be needed but from my research, they don't exist. The ideal laser source would be a fiber laser. They are simply a cluster of LED's and the fiber that couples them together is the laser gain medium. The fibers then feed into a delivery fiber and off to the workpiece or yet another coupler to add more LED clusters. A CO2 laser would also work but they are bulky, inefficient and need a lot of cooling. I work with both NdYAG and fiber lasers so I know the industry. And the industry for fiber lasers is a patent minefield. So good luck getting a cheap 500+W fiber laser. Our 4kW IPG YLS-4000 ran us almost $300,000 including chiller, fibers and beam delivery head.
From the laser you need a galvo scanner to scan the beam around the powder surface. The galvo scanner might actually be an easy hack using cheap galvanometers.
Electron beam sintering. As crazy as it sounds, EB sintering is probably the better way to go. You don't need shield gas and the purity of a vacuum leads to higher quality parts. The only issue is again cost and bulk. You need a vacuum chamber of sufficient size and a decent pumping system including a high vacuum pump, either turbo or diffusion. Though I bet you could build one the size of a larger mini fridge. The electron gun is simply a tungsten wire or ribbon and the beam is deflected using what is analogous to the deflection coils in a CRT. And we all (well mostly) should know we can scan in the 10's of kHZ so printing can be very fast. A 60kV power supply of about 5-10mA would suffice (about 600W). All you would need to do maintenance wise is keep a stock of filaments, keep the chamber door seals clean, ensure your vacuum pump oil level is good and have plenty of powdered metal. The expensive part is the vacuum system could cost well over 10 grand.