Since we'll be moving away from the 4-2-5 that we overused last year, I don't know why he wouldn't go ahead and start implementing whatever he really wants. But, yeah, common "wisdom" seems to be that you can't implement a 3-4 from scratch in one season. We won't know what Sunseri thinks about that til practice starts.
My first prediction is: no matter what we run next year, Maggitt gets at least 6 sacks.