Atcheson (18) & Litherland (19) look to me to be capable of becoming Championship standard (at least) centre backs. I expect one of them to be in the first team squad next year as 4th/5th choice, and the other to get a League 2 loan.
The academy players with the most potential are probably Tyjon, Dunn & Higgins, who are still 16 (although Tyjon turned 17 a week ago) so too early for them to be loaned out. Obviously the first 2 of them have only 1 year left on their current scholarship deals, and the other has yet to even sign a scholarship deal as things currently stand
As well as the 2 full backs that you have mentioned, Powell (19) also looks like a decent attacking left back. Others that we may see in the next couple of years are England U18 keeper Nick Michalski, & young midfielders James Edmondson (19), & Harley O'Grady-Macken (20)