If you plan to do any air traveling, then couplers are a good idea. I've flown ten round trips so far in the past three years with my coupled fixie, and I've probably paid a total of $100 in excess baggage fees (usually on airlines that charge $25 for the first checked bag). Had I taken a normal bike, I'd probably have looked at $100-200 per round trip. The couplers added about $750 to the frame price, and the case is another $300, so it doesn't take long to amortize. I think it's even more worthwhile on a tandem, despite paying the extra $2000+ for the three sets of couplers required, not to mention the two cases you'll need.
One fringe benefit of having couplers installed is that only competent framebuilders are allowed to build with S&S. The builder has to be certified by S&S before they can do any installations. and this involves having to send a sample of a brazed S&S coupler to the company. So this is another small indication that you're dealing with a reputable builder.
So for Chinese-built frames, I would check with S&S to make sure the manufacturer has actually been certified! This is grist for another mill, but I am reluctant to offshore the building of my frame because it's something I have control over. This is why I had my fixie built by Rodriguez in Seattle (with a fork by ENVE), and it's also why I would never buy a Cervelo. Yeah, it's engineered in Canada, but the actual building is off-shored to China. Screw 'em.
Luis