Actually, it doesn't have to. They could do a stock swap with present Yahoo shareholders. They can spin the shares into a separate company, and given those shares to the current share holders. There are plenty of tax advantaged games they could play.
Besides that, taxes are only a problem when you sell. If you look at the Yahoo Japan and Alibaba investments in terms of lookthrough earnings with all earnings held by the companies, the tax hit doesn't matter in the short term.
To qualify as a tax-free spinoff, the parent company must own a controlling stake in the company to be spun. Yahoo does not own a controlling stake in either Y! Japan or Alibaba.
However, there is a tax maneuver being considered, called a "cash rich split off" [0]. Yahoo would do a tax-free swap of its Alibaba shares for a 5-year historic business owned by Alibaba. This historic business can have as much as two-thirds of its assets consisting of cash. Warren Buffett did something similar with his shares in GHC.
One question is why did Yahoo not pursue a cash-rich split off in its 2012 transaction with Ali? I would argue that it's most likely for political reasons. As unfair as it may be, the optics of Jerry Yang and Jack Ma teaming up to deprive the US Treasury of tax revenue is very different from the optics of Warren Buffett and Don Graham doing the exact same thing. I think they might still pursue it, just because that's a lot of money to leave on the table.
I am almost positive that does not work, though if you can provide precedent I am all ears. And again, yahoo would be taxed on those earnings before they could return the money to their shareholders.
Besides that, taxes are only a problem when you sell. If you look at the Yahoo Japan and Alibaba investments in terms of lookthrough earnings with all earnings held by the companies, the tax hit doesn't matter in the short term.