You won't get point clouds from panorama style Tech Preview photosynths.
In Spin, Walk, and Wall style Tech Preview photosynths you can open the debug panel by typing 42 into the viewer after clicking Play.
In the debug panel, check the pointCloud checkbox and then refresh the page.
Once you've done that in a browser, the site should remember your setting.
From then on you should be able to see the point cloud in addition to the camera positions when you type C into the viewer to enter global camera mode.