I'd rather see him as DM in Masons role. For Wales he played as CB in a back three which is completely different to the CB in a back-four formation. For me he's exactly the right type of player for DM, combining both defensive stability and high workrate.
Would love to see Poch trying him there (e.g. in test games in Summer).
Issue that this raises is that you're then opening up the possibility of Rose's work rate falling off. Keep Davies at LB if only to continue to motivate Rose. Though I do think Davies is a better CM option than Dier.