3. Mon Mothma
Mon Mothma was a key member in starting the Rebellion, so exploring some of her history could make for a very interesting movie. The problem though is that after a younger version of the character was already introduced in Revenge of the Sith, so a slight retcon might be needed to make her age sync up with Felicity Jones', especially if she plays Mothma at a point in time somewhere between that final prequel and the events of A New Hope. If the rumours that this Star Wars spin-off will focus on bounty hunters hired by the Rebels to steal the plans for the Death Star are true, having Mothma actually join them would reveal a new side to the character and make for a very unique scenario as the leader of the Rebels finds herself mixing with all types (possibly even Han Solo) to get those important blueprints. The age thing is definitely an issue, but they could make this work somehow.