Printing is funny term to use as it isn't strictly printing. The technique has been around for a while (easily 20 years) but it used to be very costly and you are left with a solid model of course. Then again a sprue is a "solid model" so as long as the goal isn't to produce a finished model which has an inside as well as an outside then it must boil down to relative costs.
Actually a lot of computer generated model designs now produce the sprue (male form) design digitally. With this in mind the digital design can be transferred to a metal or resin injection moulding tool (imt) to produce the intaglio(female form) for multiple manufacture of injection moulded kits or figures. The process would thereafter be similar to what happened in Airfix's old factory in the 50s using polystyrene or polyethylene granules liquefied with heat and pressure and forced into a two part "mould".

The other approach is to forget about the imt or injection moulding and produce the sprue or model using a computer controlled device that hardens or subtracts zones of a material (eg uv curing photopolymers) or accurately sprays or deposits a material in 3d space(additive manufacture) or molten polymer deposition as it is known. SHS- selective heat sintering is likely to be the best bet for the hobby as the finished product would be a familiar plastic rather than a resin or a metal. It would basically build up a model in tiny slices and to contradict myself you can could get an inside and outside of sorts. How would modellers feel about a cubic sprue? I can only guess the sprues would look different as you don't have to contend with flow and pressure with SHS. I am not sure of the financial aspects for the continued preference for traditional injection moulding but as mentioned earlier cost is a huge factor. The more companies that use 3D printing then the prices will come down and in the blink of eye it becomes mainstream.
To directly answer Martin
Soon- could be several months or a decade
cheaper - as above
accessible - things that catch on soon become accessible
Shorter times from initial idea to sale of product- At the moment it seems to take as long to produce a sprue of plastic figures from concept to box on the shelf as it does a blockbuster film or game. That is also one of the nettle leaves to be grasped.
Obviously our niche of niche hobbies will follow whatever happens but I can see 3D printing satisfying some of the imperatives that made the internet what it is today. Then it could be days we have to wait rather than my months.


David