Is it safe to assume from the FAQs that WorldPerks Platinum and Gold elites are not eligible for the 50% standby fee reduction extended to our OnePass brother and sister elites?
Will anyone other than OnePass Gold and Platinum members be eligible for the half-price $25 fee?
No.

to CO for abandoning fee-less standby travel. I can't envision any scenario where allowing a passenger to standby and claim a seat that would have otherwise gone out empty on an earlier flight is anything other than a win for the airline given that it frees up a seat on a later flight that may eventually get sold.