Keller will be a significant upgrade over Taylor. Taylor is a gamer, and a tough smart kid, but he lacks some of the physical tools you look for in a top flight QB. Keller is going to be a first day draft pickin the NFL, maybe even first round, and has a year to run the scout team and learn the offense. He's going to be a beast next year, with all of the RBs and WRs back, and an improved O-Line. Look for the offense to be very explosive.
On defense, we graduate the entire D-Line, but have some great talent behind them that have gotten some reps. So we'll have a younger but more talented group there. At LB, we lose Bradley and Mckeon I think, but keep Ruud, Octavien, and a ton of depth. Again, we lose some experience, but have a more talented group overall. In the secondary, Bowman should be back, which is immediate upgrade. He's a heck of an athlete, and can shut down the opposing team's best WR. His return moves Grixby to nickleback, a position he's much more suited for.
The stars of the team on offense will be Keller, Lucky/Jackson, and Purify on offense. On defense, Octavien and Bowman will be the playmakers. I expect a Top 10 finish and a run for the National Championship next year.