As someone who writes a lot of glsl (for effects for a video editor, not for 3D), I ended up writing my own preprocessor to include dependencies (and to "patch" differences between GLSL ES and regular GLSL). Package management is the next logical step, so I personally don't see a problem with it.
It's like anything, you're not just going to dump a third party library into your code and hope for the best. You're going to see if it does the job, does the job well, and if it doesn't - you'll figure something else out.
This is something I really miss from a few years ago when I was using Cg to do my shaders. It had (what I would consider) fairly basic features like #include and the ability to specify texture states and so on within the shader file. Now I have to do all of that manually, or write my own preprocessor or something...
It's like anything, you're not just going to dump a third party library into your code and hope for the best. You're going to see if it does the job, does the job well, and if it doesn't - you'll figure something else out.