Sandisk's remarkable stock performance has positioned it as a leading candidate for inclusion in the S&P 500, potentially overshadowing MicroStrategy. The Western Digital spin-off, focused on NAND flash and SSDs, has seen its stock soar by 515% over three months, reaching a market capitalization of $40 billion. This surge has made Sandisk the dominant component of the S&P SmallCap 600 index, with a 2.6% weighting, far surpassing other components. Despite MicroStrategy meeting the quantitative criteria for S&P 500 inclusion, it was excluded in September, raising concerns about the index's approach to crypto-driven valuations. The next S&P 500 rebalancing is set for December 19, with Sandisk emerging as a strong contender for promotion.