Baidu is already the most popular web search engine in China, having gained market share hand over fist after Google decided to abandon the Chinese mainland and move its search servers to Hong Kong. Apple most likely sees this as a way to try and increase their popularity in the Chinese mobile phone market, where they have lagged far behind the many forms of Android (both forked and official). The fact that it will not provide Google with a way to grow its market share of Chinese mobile search is in all probability just a bonus.
Despite having smaller market share in China than elsewhere, the sheer size of the Chinese user base lead to the territory growing to become Apple’s second largest market last quarter, behind only the United States; as such Apple and Google undoubtedly view China as an extremely important battle field in the ongoing war over mobile market share.
According to Bloomberg’s sources the announcement could come as soon as next week, perhaps during WWDC. As an interesting quirk of history, way back in 2010 none other than Motorola chose to replace Google with Baidu as its default search engine on its Android smartphones; presumably they reversed course at some point!
As you might expect, no one at Apple, Baidu, or Google wished to comment on the story.