I wouldn't over invest in 3D printing. It will be like the car industry where everybody jumps on board, but there ends up being only a handful of big winners.
3-5 years, maybe longer- as much as 10+ years? I'm not sure. It depends on the industry's overall growth. If it remains strong at a CAGR of 25-30%, then probably yes.
By that time (10+ years) there should be quite a few new entrants into the market that are publicly traded I'd think.
re: What kind of time frame do you give yourself for your 3D portfolio?. You think you'll be investing in them for the next 10+ years?..