I'm actually not at all against moving Washington to OT. I was super intrigued by him when they drafted him. I thought he could be a secret weapon, but he's just way too slow and lumbering to ever be anything more than a blocking only TE. I don't think he has much time left in the league at TE, so it's worth a try.
I get becoming a T is not an easy ask, but he's not an ordinary TE. He's a physical freak and essentially already playing OL. He'd have to put on some weight and they'd have to work with him, particularly in pass blocking, but given his size, athleticism, and blocking ability already, I don't think it's that far fetched.
Plus, if it worked, they could move Fautanu inside which is what a lot of people projected was his long term position anyway. He's not going to be the starting RT next year or anything, but start the process now. If it doesn't work, oh well. They didn't lose much by trying.