Friday's hotly anticipated SpaceX public debut could prove a defining moment for capital markets — and be a "referendum" on Elon Musk's leadership, according to market watchers. Musk's eye-watering $1.75 trillion valuation target reflects a price-to-earnings ratio of almost 100-times, compared to around 20-25-times for chip giant Nvidia and roughly 10-times for Apple. Nasdaq has recently introduced rule changes to make it easier for SpaceX and other firms planning mega IPOs to list on the...