A big reason why I wouldn’t try for an extension in this case is due to Walker’s age. By the time he will be eligible for free agency, Walker will be 31 years old. An extension will buy out 1-2 years of free agency. This isn’t like Andrew McCutchen, where an extension buys out prime years 29-31. The Pirates already have most of Walker’s prime years under team control.
This is the main reason I agree. Walker obviously isn't nearly as good as McCutchen, and he spent a lot more time in the minors than McCutchen did. Because teams get to control their players' salaries for their first six to seven years in the league, the Pirates already have Walker under control through his age 30 season, so if they were to sign him to any additional years (usually a big reason teams sign young players to long-term deals), that time frame wouldn't start until he was already 31. In addition to not being as good a player as McCutchen is, Walker isn't as athletic or well-rounded as McCutchen, which makes him the worse bet to age well.
For all those reasons, I'll stick with what I wrote last year and agree that Walker probably shouldn't be extended unless he's willing to sign for well below market rates. Something like a two- or three-year deal to give the Pirates cost certainty for the next few years they already control would be one thing, but a longer deal designed to keep him in Pittsburgh for a couple extra years would be something else.