Don’t think he would want to be part of the Kingdom and then go about killing Christians after Christ’s reply.....Paul was trained to be a Jewish lawyer (educated in the Scriptures)..he was not a rich young ruler..
The question would be, a ruler of what. Not in the secular governmental sense, but Paul would be considered a maven of mavens in Jewish circles. His views would have great clout in matters of expected religious practice. Think the Lubavitcher Rebbe.