I hardly think Illinois offense is a 'one-trick pony'. They run multiple layers of actions, its a pretty sophisticated spread/5-out continuity framework. If the primary action can't render a positive result, it flows immediately into secondary and tertiary options like slot cuts, "cut and slide' weak side movement, or pinch-post (and more). I loved the ram screens this year, they'll do more of that for sure (Purdue/Smith got cooked via ram screens; couldn't figure it out). Lot of improvisation as well, which is honestly what you're asking for: its the one thing teams can't game plan for. They can know a player's tendencies, but never on any given play can they read it because there's very little that is hard-scripted.
The offense isn't rocket science: its actually one of the more complex ones out there. There is this misconception that we basically just run ISOs all game; not true at all. Again, lots of improvisation, read-and-react, recognizing space and making decisions on where to drive / cut / move, utilizing nuanced concepts like ghost cuts, inverted screens, and the high-post playmaking that flips the defense upside down (bigs leave the lane, and our lengthy offensive players now have to score over 6'3" guys instead of 6'11" guys).
What the Illinois offense is not, is an ISO-every-play offense that a lot of casual fans get duped into falsely identifying it as (probably due to it being ISO heavy, but even ISO actions have nuance to them and aren't necessarily minimalistic in nature).