Okay, I took a deeper look at this. Form 8888 still exists (https://www.irs.gov/pub/irs-pdf/f8888.pdf), but it's changed to no longer allow you to buy I-Bonds with your refund. Now it's only used to split federal refunds to multiple bank accounts.
Per Pub 17, "Purchase of savings bonds discontinued. The program allowing for your refund to be deposited into your TreasuryDirect® account to buy savings bonds, as well as the ability to buy paper bonds with your refund, has been discontinued. Form 8888 is now only used to split your direct deposit refund between two or more accounts or to split your refund between a direct deposit and a paper check."
Your original post didn't mention I-Bonds, just the form #, so I was confused as to what you were asking about.
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