Most seem to agree the DL is the biggest question mark for the defense, though I wonder if the question mark is really the interior DL. At DE we have massive amounts of talent:

Corbin Kaufusi, 6'9 285 (JR): played far more last year than most anticipated after transitioning from basketball; he made some great plays with his long frame; really excited to see his progress
Trajan Pili, 6'2 245 (SO): only played a little this past season but had several TFLs and showed flashes
Sione Takitaki, 6'2 245 (JR): everyone is anxious to see him back on the field as he has shown the ability to make big plays; hopefully his body holds up after being away from football for a year and a half
Uriah Leiataua, 6'4 265 (FR): sounds as if his redshirt year was a good one where he got his body back and gained some good weight; was a huge recruit who many are anxious to see in action

You also have Moses Kaumatele who started three games last season and Langi Tuifua who was one of the most prized recruits from the 2017 class. Other possible contributors include true freshman Lorenzo Fauatea and converted linebacker Rhett Sandlin. There are eight guys who could make meaningful contributions at the DE position this year, and they are all underclassmen.