I agree with you about it's one thing to win the ball from a defender than a foward. But if he's ever going to be deployed as a fullback I think vs NE would be the best opportunity.
It shouldn't be, but the transition always isn't as seamless as a lot of people are saying (see Sal Zizzo). Winning the ball off of defenders through a high press is a lot different than defending skilled strikers 1v1 and keeping on the same page as your other defenders. Someone mentioned in another thread that they thought he could be a USMNT quality fullback, there's a huge gap between that and the subpar MLS winger that he is now. Guys like Yedlin and Rogers were leaps and bounds ahead of Muyl in ability when they made that transition, and even they took some time to adjust. Not to say that it can't work for Muyl in the long run, but in a perfect world he'd have some time with RB2 there to make sure its actually a fit.
The have speed and while Muyl isn't Taxi speed wise I think he does have soccer IQ to know how to contain and usher a dribbler to a disadvantageous position ti then close on him and out muscle him for the ball. He's done it to midfielders.
I just think that Zizzo had a bad game so much so that this is worth a try and combined with my opinion that Etienne and Veron did better and so did Royer it's worth starting those 3, dropping Zizzo and trying Muyl at right back. Now if it was a big game like say MLS Cup Final I'd hope we'd have Murillo there. But it's early in the season, the next game is a cup game but against a team that can't finish. Now is the time to try this. To try to play with a midfielder of Veron, Royer and Etienne, with Muyl at right fullback and maybe play Sacha next to Felipe.