Indiana-Illinois is bigger than Nebraska-Michigan
I'm not sure that this is as laughable as 
@FearlessF thinks but it is definitely up in the air.  
In theory #9 Illinois at #19 Indiana is a HUGE game but this early in the season, who knows.  
I think Michigan/Nebraska is arguably bigger mostly because Michigan's schedule is extremely easy.  Of the B1G's currently ranked teams the Wolverines:
- Host #1 Ohio State on 11/29
 - Do not play #2 Penn State
 - Do not play #6 Oregon
 - Do not play #9 Illinois
 - Do not play #19 Indiana
 - Travel to #25 USC on 10/11
 
Other than this game and the visit to SoCal, the Wolverines visit MSU, NU, and UMD.  They host UW, UDub, PU, and tOSU.  If they win this, 7-2 should probably be seen as their floor (losses at USC and vs tOSU).  That might get them into the CG mix and upsetting either USC or tOSU to go 8-1 would almost certainly get them in.  That makes this game a big deal.  
On the other side of the ledger, Nebraska has a pretty lightweight B1G schedule as well.  Of the B1G's currently ranked teams the Cornhuskers:
- Do not play #1 tOSU
 - Travel to #2 PSU on 11/22
 - Do not play #6 Oregon
 - Do not play #9 Illinois
 - Do not play #19 Indiana
 - Host #21 Michigan on Saturday
 - Host #25 USC on 11/1.
 
It is a similar story for the children of the corn.  If they win this weekend they'll probably be favored in every remaining game except PSU.  That makes 7-2/10-2 or 8-1/11-1 into very realistic possibilities.  
I do think that IL/IU is a huge game.  Both of them have CFP potential but I think they have more remaining decent tests.  Illinois still hosts #25 USC and #1 tOSU and has a West Coast road trip to Seattle.  Indiana still has to travel to both Eugene and State College for two road games against top-10 teams.  
Where I think IU/IL is important is that the winner gets some relief while the loser probably needs a big upset.  Indiana isn't getting into the CFP at 6-3/9-3 with losses to the only ranked teams they played so if they don't beat Illinois at home they'll have to find a way to upset either #6 Oregon in Autzen or #2 Penn State in Happy Valley.  Good luck with that.  
Similarly, I think that Illinois has zero chance at 6-3/9-3 with losses to the only ranked teams that they played.  They might not even get in at 7-2/10-2 with losses to IU and tOSU and a home win over USC so if they lose this they absolutely have to beat USC and they might need to spring an upset on the Buckeyes in a few weeks.  
FWIW:
Illinois' last five wins over Ohio State came in Columbus (2007, 2001, 1999, 1994, 1992) so they haven't beaten the Buckeyes in Champaign in over 30 years (1991).