Is it possible for an Eastern rite Catholic to be elected pope? Has there ever been one?
Yes, it is possible. In the history of the Catholic Church, there have been at least ten Easterners elected as Pope. Each one became Patriarch of the Latin Church, and celebrated the Roman Rite.
When all is said and done, I think that it is preferable that the Pope belong to the Latin Church. Why? Because the Pope, by definition, is the Bishop of Rome. And by tradition, the Bishop of Rome is Patriarch of the Latin Church.