They undoubtedly will add someone at quarterback, someone capable of competing with Hurts and potentially winning the job. The Eagles view the backup quarterback spot as a top-15 roster position, and for good reason. They won a Super Bowl by having a more-than-competent backup to Carson Wentz.
So now without Wentz, they need someone to complement, supplement, and/or supplant Hurts as the presumed starter. They could draft that player, they could sign a veteran, or they could trade for someone like, yes, Nick Foles.
Whatever they do, the Eagles will do something more than retain a backup who is expected to embrace that spot and not truly challenge the starter. Although Hurts won the one-on-one against Wentz, Hurts still may not be the starter when Week One rolls around.
So while the Wentz trade becomes the ending of the starting-quarterback search for the Colts, the transaction may be just the beginning for the Eagles.