I think he's already hit the ceiling at 10 wins but its tough to say that that really is the ceiling. By my math, not counting 2020, PJ's teams average 7.25 regular season wins. 2019 and its 10 wins seem to be an outlier although I'm no statistician and maybe 2019 isn't statistically significant. If we throw out 2019 (best season) and 2017 (worst), the win average falls to 6.83.
I don't count the bowl wins because we're talking about ceiling and presumably for most, that means making the CFP and in that scenario, only regular season wins matter. And if 2019 is an outlier (and really, the monumental changes in NIL and House that have occurred since then really make 2019 an outlier), it seems like the ceiling might be 8 or 9 wins. Unless and until there's a big influx of NIL into the program, it seems like we are entrenched solidly in the middle of the B1G, maybe the half of the middle third.