I assume you're talking in wins, because we've already seen a ton of progress in many areas. A team can get better on the field and it not result in more wins, for a variety of reasons. It's exactly what I'm predicting for Purdue, for instance. I think they'll be better but because they overachieved in wins last year I think they'll post a similar record.
It's possible to be better and still only go 4-8 if things like injuries go against us. On the other hand, if things fall in our favor, 8-4 is also possible. There's a lot of fortune that goes into this game. Mike Riley's first two years are very similar, performance wise, but two very different records. Northwestern are posting 10 win seasons followed by a drop, but those teams are all around neutral in terms of yards per play differential, it's the games many bounces that is accounting for the change in record.