What is challenging with point-rendering?
Filling the holes. Previously, the 3D- scanner devices were not as fine as they are today. Hence, relatively lesser number of point samples were available. That made surface reconstruction ( building a triangle mesh over the points' surfaces and eventually render the triangles ) much more suitable that direct point rendering. However, today, the number of samples that are captured are much larger.
Symposium on Point-Based Graphics is a conference that is dedicated to point-based graphics! Interesting!!