Amid all the hype over Alibaba's planned IPO, one detail has been overlooked. The blockbuster deal, which could be the biggest Internet IPO ever, apparently won't include the Internet giant's fastest-growing business, the money market fund Yu'e Bao.

Launched less than a year ago to capitalize on the cash balances that merchants leave in Alipay, the e-commerce company's online payment system, Yu'e Bao has grown at a phenomenal rate. At the end of March, just nine months after it opened, the fund boasted 541 billion yuan, or $87 billion, in assets.