I'm assuming that Metcalf will get to the point where his form is irresistible and forces Walker back the centres, but it might take an injury for him to get his shot.IMO Metcalf is not a reason to fix something that is not broken. Walker looks real good towards the end of last season. I expect injuries will determine who gets a shot and when.
His defense probably still needs a lot of work, as might his passing. But from what I saw in the 9's his speed and his game sense are massive assets. Once he is ready for FG he will become a mainstay, I think.