My first shade cloth will be starting its fourth year and the green one will be starting its third. I don't use shade cloth from the end of October through February. Both shades are doing fine. Brittleness would usually be the first sign of breakdown, where the "plastic" fabric will begin to tear. It is over for the fabric then.
If/when I expand my porch and make it a sun/Florida room, I have a feeling I will need some shade fabric. My plans are to have 8-10' of glass overhead and the entire outer (east exposure) "wall" will be glass. That wall will be 32' long and 9' high. I don't know how I will shade what glass needs shading. Hopefully the glass experts will have an answer for that. Aluminet may be and answer.
This is why I need a larger, climate controlled sunroom. Here's the porch this week.