Maybe, Apple has a surplus of that aero-nautic grade glass they use to make the iPhone screens? Personally, I would hate the idea of this glass trackpad to be a tiny monitor like an iPhone for a number of aesthetic and practical reasons.
1) It's "un-Apple" and gimmicky
2) It would probably tax the GPU
3) I already look down enough at the keyboard to look at what I'm typing - I don't need to look at the trackpad, too, to see what's suppose to be displayed there.
Anyway, this is fairly consistent with previous rumors about the new MB looking more in line with the iMac, which has a glass cover and the MBA. The glass on the iMac is breakable, btw and is held on by magnets. I could see the glass trackpad on the MD to be held on by magnets too. The same magnet that keeps the notebook closed. People can then take out the glass on the trackpad and use it to snort coke. j/k. I really can't see this new design, yet, but I hope they don't mess up the simplicity of the current design. Adding aluminum would have been enough for me, along with the new specs. And, maybe LED. But, I'm not in the market for a new laptop anyway as my 12" PB is still going strong.