From a scheme standpoint, this is what I'm most excited about because the weakness of Leonhard's scheme has been defending the 11 personnel scheme. The 2-4-5 that they've used has not worked against OSU or Minnesota. The 3-3-5 is a much better matchup at controlling the LOS while still having the DBs to defend 3 WR, and UW will have better DL than Cinci to be able to effectively use 3 DL. I think the 4-2-5 is best, but UW doesn't have the DEs on the roster right now for the 4-2-5 unless Witt's foot miraculously heals and Thompson drops a little weight to become more agile.
As for the big nickel, they have plenty of guys who can do that - Austin Brown, Preston Zachman (who was initially recruited at LB), Cade Yacamelli, Hunter Wohler (6'2", 210), Jake Ratzlaff, and Aiden Vaughan.