Elon Musk is mulling whether to place all Twitter content behind a paywall, according to a new report. While any such change does not appear to be imminent, Musk has recently been turning over the idea of a sitesubscription fee with one of his advisers, venture capitalist David Sacks, according to a report from tech newsletter Platformer. Lots of questions remain around the potential paywall for the platform, the biggest among them being who will be charged and just how much. A source familiar with the discussion told Platformer one option includes keeping Twitter free for a certain amount of …