This is the CIE "chromaticity" diagram and in this case, the triangles appear to show the difference between the gamut of a 3-laser-based display (larger triangle) and the standard BT.709 color gamut (smaller triangle). The xvYCC gamut includes all (or virtually all, depending upon who you ask) of the entire horseshoe, in other words, virtually all human-visible colors, so it would not be limited to any triangle on this chart.
That's actually the advantage of xvYCC and explains why HDMI chose that standard rather than one of the other "extended" colorimetry standards; xvYCC really does encompass anything that future display technologies might be able to throw at us.
In the laser case, because lasers are pure, single-frequency sources, they exist right at the edge of this horseshoe. If you imagine a 4-laser display with the 4th being 2/3 of the way up the left edge, you can see that lasers have the potential to display a huge portion of the visible colors, much larger than anything else, including LEDs, which, though they are placed outside of the BT.709 triangle, still cannot reach the very edge like lasers.