According to WhoScored Sam Byram has played at right back in just two of his 15 starts this season (FWIW they've only given him an average rating of 6.65 from those games too.). It appears for a long time his weaknesses were ignored due to his youth but he's now 22 and now has over 130 league appearances for Leeds so he can't just use his age as an excuse anymore. Especially in the Premier League. Don't get me wrong he's not a bad player and I know he'd only be a back up but I just don't think he's quite as good as everyone thinks, can be quite shakey defensively at times.
Coleman is only 27 and it's not like he's been chased by the big dogs anymore so realistically I can't even see Byram becoming a starter. Will he be happy to go from starting every game to only being a back up? May be a little different if we made Europe every single year and needed a big squad but unfortunately that hasn't been the case over the past several years.