Shanghai-based Ximalaya Inc, an online audio platform on the Chinese mainland, has filed for initial public offering in Hong Kong, suggesting investors may be confident about the future prospects of the burgeoning niche media market. Ximalaya provides a wide variety of audio content through which people share knowledge, information or entertainment. It boasted 262 million monthly active users as of June. The size of the float has not been determined. Ximalaya had earlier dropped plans to list in the United States. The company reported revenue of 2.51 billion yuan ($389.8 million) for the first half of this year, up 56…