According to trusted aviation insider JonNYC United Airlines will introduce mileage pooling. Members will be able to join one pool and add miles to a collective account, the pool leader can then determine how those miles are used. Aeroplan previously offered this but has suspended family sharing, whereas JetBlue, British Airways & others all offer variations of this. I assume there will be some preventative measures that aim to stop things like selling miles and accumulating orphaned points (e.g transfers of at least 1,000 miles).