I'm actually very tempted to have Darnell Washington put on more weight and be a tackle. I think his upside in terms of league worth ($$$) would be higher at that position.
I think you could make a case that there's less risk of him failing to come on as a blocker at tackle than him failing to come on as a pass catcher at tight end/wide receiver.
Remember that in this league the dominant tight ends play about as much wide receiver as they do in-line, and they catch a lot of balls and make an impact that way. Is that what Darnell Washington is destined to do? Hard to say, as he spent his whole career at Georgia embracing his role as an elite level blocker, only began to really explore what he can do in the passing game later in his career and had to play 2nd-fiddle to Brock Bowers. How much does he come into the league being able to impact the passing game? How much can he learn it, particularly being such an exaggerated long-strider as an athlete? These are fair questions.
On the other hand you look at what he's been for his entire career at Georgia, which is a blocker, a 3rd tackle. If you don't consider that simpatico with what he'd be asked to do if he made the transition to tackle at the NFL level, I don't know what to tell you. It's what he was. You could make the argument that he comes out of Georgia having more experience as a tackle than as a pass catcher, and that the shortest distance from A to B with him is actually as a tackle.
When you put that together with the higher impact ($$$) potential as a tackle than as a tight end, I'm surprised the player himself hasn't expressed a preference. But I do know for a fact that several NFL scouts currently are factoring in a potential move to tackle into their evaluation of him.