My thought is start Tyrod for a maximum of 3 more games. If he doesn't improve significantly (which seems unlikely) then hand the keys over to Nate at the bye week. Let him participate with the starters for two weeks. Then start him for the remainder of the season. Lets see what we have. Its entirely possible he becomes our franchise guy. If not, its clear what direction we take next spring.
EDIT: I route hard for Tyrod but the more I watch, the more I conclude his ceiling has been reached.