Creep is the reason you don't see plastic handlebar shims. Nearly all polymers, including Delrin, flow a bit under stress. This flow is called creep, or sometimes stress relaxation.
If you installed a Delrin handlebar shim and tightened the stem bolts to the manufacturer's designated torque values, your handlebar would work just fine. For a while, anyway. Over a period of days or weeks, the Delrin would flow (a tiny bit) out from under the clamp area, effectively loosening the clamp bolts.
You would probably discover the wonders of creep when gou rode over a bump on your hoods and your handlebars rotated ~80 degrees forward. You may or may not fall when this happens, but if you did, it wouldn't be pretty. DeeHubs suggested you'd lose a lot of teeth. This is plausible, but I think you're just as likely to break your collarbone (potentially losing teeth as well).
But DeeHubbs recommnded dental implants to save weight after your crash. He's relatively new to this forum, and so his suggestion is a little naïve. A true weight weenie would leave those heavy teeth on the road without replacing them. That's a lot lighter than even implants, and the $/gram ratio is off the charts.
In all seriousness, a properly installed aluminum shim should be fine. But don't mess with polymer shims for handlebars.