Robin Wigglesworth Financial benchmarking giant MSCI is working on an “ultimate index” tracking the performance of all markets, which could mark the culmination of half a century of academic theory and practical financial engineering. Indexing is a booming business, slicing markets up into geographies or categories such as equities or bonds, and then subdividing further by size or industry. These are then used as benchmarks for fund managers, or packaged up into investable products. But a way to combine everything from commodities to...