I noticed Google Earth uses skirts as well
In video games tears weren’t noticed due to ‘smearing’. Such as http://quakewiki.org/wiki/gl_clear , set ‘gl_clear 0’ and screen pixels simply retain the color they had previously if not painted this frame. This hid small tears well because it ‘smeared’ neighboring pixel colors so one doesn’t even notice the tears. When nocliping you’d set ‘gl_clear 1’ to disable smearing, if a pixel isn’t painted it will get painted with a default color.
Is this smearing technique possible in Cesium instead of using skirts? One problem is that it can’t simply be the entire view-port, you don’t want mountain edges smearing where sky should be drawn, for example. Somehow it would have to distinguish tile edge tears from terrain/sky edges, which might be difficult.