You don't need to hold and transfer the cash immediately with T+2 settlement because effectively your broker is lending the cash to you for 2 days with the shar

You don't need to hold and transfer the cash immediately with T+2 settlement because effectively your broker is lending the cash to you for 2 days with the shares as collateral, hence the margin requirements and the RobinHood debacle. But there's no fundamental reason that loan must be made by your broker, aside from the historical T+2 convention. You could just repo the shares for two days while you wait for the cash to arrive.