I'm a bit confused, are SNA and GLAMOR competing projects within Intel? What's the logic/history behind the two?
Glamor translates 2D drawing commands into standard OpenGL and runs it on the 3D driver. As such, it's a generic implementation that any driver can hook into quite easily.
SNA is a highly hardware specific optimized solution, currently tied closely into Intel chips. It has heuristics in it that try to determine whether an op should be passed into the GPU 3D hardware, 2D hardware, or performed on the CPU. That can vary between GPUs.
SNA was started a while ago to try and wring out any extra performance possible from Intel chips. Glamor started later on, as people thought that SNA was too complicated and should be dropped, but it seems that SNA has caught on with some people and proven itself good enough that Intel will likely go that direction. But it's essentially a fair amount of work that will have to be done every time they bring out a new GPU generation, while Glamor would basically just work without much effort.