I looked up the largest universities by enrollment and eliminated the non-D1 football schools. It's not a perfect list because there are some big schools that don't fall in the category. Some on the list might not be D1, but it's a start.
If we go to a four league 16-team "Super Conference" idea, here's the list of the top 64 plus a couple more:
| D1 Football School Size | University |
| 1 | Arizona State University |
| 2 | Ohio State University |
| 3 | University of Central Florida |
| 4 | University of Minnesota |
| 5 | The University of Texas at Austin |
| 6 | University of Florida |
| 7 | Texas A&M University |
| 8 | Michigan State University |
| 9 | University of Washington |
| 10 | Pennsylvania State University |
| 11 | University of Illinois at Urbana |
| 12 | Indiana University |
| 13 | University of Michigan |
| 14 | University of Wisconsin |
| 15 | Purdue University |
| 16 | Florida State University |
| 17 | University of Arizona |
| 18 | University of California Los Angeles |
| 19 | Rutgers University |
| 20 | University of Maryland |
| 21 | University of Houston (UH) |
| 22 | Temple University |
| 23 | University of California Berkeley (UC Berkeley) |
| 24 | University of North Texas (UNT, North Texas) |
| 25 | University of Georgia (UGA) |
| 26 | University of Southern California (USC) |
| 27 | Brigham Young University (BYU) |
| 28 | North Carolina State University at Raleigh (NC State University) |
| 29 | University of Colorado at Boulder (CU Boulder) |
| 30 | San Diego State University (SDSU) |
| 31 | Boston University (BU, Boston U) |
| 32 | University of California |
| 33 | University of Missouri |
| 34 | University of Cincinnati (UC) |
| 36 | Texas Tech University |
| 37 | Mt San Antonio College |
| 38 | The University of Tennessee |
| 39 | University of Kansas |
| 40 | University of Iowa (Iowa, UI) |
| 41 | University of North Carolina |
| 42 | West Virginia University |
| 43 | The University of Alabama |
| 44 | Louisiana State University |
| 45 | University of South Carolina |
| 46 | University of Pittsburgh |
| 47 | Iowa State University (ISU) |
| 48 | University of Kentucky (UK) |
| 49 | Washington State University (WSU) |
| 50 | University of Oklahoma Norman Campus |
| 51 | University of Connecticut |
| 52 | Auburn University |
| 53 | University of Virginia |
| 54 | University of Nebraska |
| 55 | Kansas State University |
| 56 | Oklahoma State University |
| 57 | University of Oregon |
| 58 | Fresno State |
| 59 | Ball State University |
| 60 | University of Louisville |
| 61 | University of Arkansas |
| 62 | Syracuse University |
| 63 | Clemson University |
| 64 | Boise State University |
| 65 | New Mexico State University |
| 66 | Stanford University |