He's hitting Spring Training pitching quite well. He may warrant being placed in Triple A. I also think that, because of his swing, he'd be ready for the majors now.
Nothing wrong with having a player do well sooner than expected. As best I remember, though, Rendon hit well last spring. If not Harrisburg, let him play every day, ride the bus, get used to the pro baseball grind. Unless injuries crush the Nats, Rendon seems like a nice-to-have problem next year.