The tolerances on PCIe boards are very tight, and if you bend them, force them at an unnatural angle, teach them yoga, or anything else that isn't strictly in the spec, you have problems. It isn't that NVidia did anything bad, it is just a question of the tolerances of many discrete parts, the case, the mobos, the cards and the bridge can all add up and cause issues. So, we are in a situation where is basically works like advertised, but they don't trust it in the hands of the average mouth breather. I kind of agree with this logic.
To make matters worse, several PCIe boards have the slots in different positions, some have a 1x slot between them, others take liberal advantage of loopholes in the spec. It is hard to stretch a PCB. Expect a full lab test on SLI bridge stretch testing if we ever get out hands on one, possibly involving fire, because we like fire.
The solution is simply, design a flexible link to do the same thing, in this case a ribbon cable like connector. Expect the new design soon, but I wouldn't expect many shipments before then. When they do ship, the performance is everything they promise, happy gaming. ยต