First, 8 classes are fine...no districts...
I can't speak for the big schools, but the Friday night before the first game is a huge night for the more rural school district, who do their football scrimmages and introduce all of the fall teams, band, etc...Booster club breaks out the new t-shirts and other gear, while getting a jump start with a full concession stand and raffle ticket sales and/or other fundraisers for all school groups...Allowing scrimmages against other schools will likely greatly affect this incredibly important community event...
That said, I have no problem with preseason scrimmages against other schools, some of which might be worth paying to get into...I can just picture York & IC doing their "Meet the Teams" night separately at 5:30, with a football scrimmage at 7:30....or McNamara & Bradley-Bourbonnais...Joliet West & JCA...Providence & LWW...Lisle & Benet...nearby teams that otherwise won't play each other for whatever reason...That works really well when you can walk between campuses, but for the truly rural district where it is a half hour drive to the nearest opponent (likely a conference opponent) it would be an utter pain in the a**...
Playoff neutral sites...State finals, of course...Semis, I think so...pick 8 neutral sites for the 16 games (NIU, WIU, SIU, EIU, ISU, Northwestern, Joliet Memorial Stadium (no JCA), Soldier Field lets say)...and the finals at Illinois...use the closest schools to the site...