Uh .. the answer is NO. Some Quad-SLI motherboards do support Tri-SLI, but most do not. Most support Quad-SLI because they provide two PCIe lanes, where each lane can be used with a GPU like the GTX 690 or HD 7990 where the card by itself is already SLI or CrossFireX. A GTX 690 is not ONE GPU, but TWO. They're just combined into one PCB. So by default, that is already a SLI configuration graphics card. SLI does not mean using two physical cards; it means using two physical GPU (the chip itself). So in that sense, if you pair a GTX 690 with another GTX 690, then that would be a Quad-SLI even though it takes up only two PCIe lanes.
If you read the manufacturer's website for the motherboard that you want to buy, it will tell you straight up if it supports Tri-SLI or not. For example, the ASRock Z97 Extreme4 supports Tri-CrossFireX. But the ASRock Z97 Extreme6 supports Quad-CrossFireX, but does not support Tri-CrossFireX.
Having said that, all Quad-SLI or Quad-CrossFireX support will also support SLI and CrossFireX (naturally), so backwards-compatible logic does work in that case.