The euphoria around Rivian kicked into overdrive Wednesday as it debuted as a publicly traded company, with an opening share price of $106.75. If that sticks, it would give Rivian an implied valuation of $90 billion. The opening trade was nearly 37% higher than its listed IPO price of $78. That absolute eye-popping number makes Rivian one of the largest IPOs in U.S. history and puts its market cap above GM as well as one of its backers, Ford (GM’s market cap is $86.31 billion; Ford’s is $78.2 billion).That share price continued to rise after it began trading around 1...