That would be terrible, as many people I know play on toasters, use Graphics: Fast *and* expect pipes to work the way they do. Viewing items in pipes is a gameplay issue for us, not a graphics issue. What we do, however, is respect them in the following ways (for now):
- The effect of pipes going into a non-full-cube block fully (like a chest) is only enabled in Fancy mode.
- Robots emit less particles if the Particle setting is changed.
What we could do for Fast is work on ways to make the item rendering in pipes less intense, for instance disable the enchanting overlay OR make items in pipes only visible from up close. (I'm also talking to Player about potential ways to write a "fast" item renderer to fit the basic use case) But we won't just make all pipes opaque - that's a gameplay change, not a graphics change.
EDIT: Also, keep in mind Minecraft itself respects Fast graphics rendering and makes item rendering, well, less precise.