YIKES is right! You really need to think about this.
It doesn't seem like a good idea at all; glass resonates like mad & the sound would be anything but neutral.
Why a component rack shelf would be made of glass (some are) is completely beyond my comprehension as well.
I remember back to an old wooden rack I once had (this was heavy furniture, not an audiophile quality design) which had hinged glass front doors. Actually it was a pretty decent rack though.
I had to remove the glass doors & hinges in order to squeeze in a new wider component. After a few days listening & testing I was satisfied, & decided to reinstall the glass doors. Fired the rig up again & it sounded really bad. I thought I broke something, but everything seemed to be working; just sounded awful. I couldn't believe it was the doors, but I hadn't changed anything else so I removed them again & all was well. Yesiree Bob, glass is the problem, doors open or closed was even worse. Just tap your knuckles on anything glass & listen to it ring (oscillate).
Acrylic seems like a much suggestion; it just thuds when you strike it.