Out of curiosity, I went through Marathon Guide's "top BQ" races from 2023, and picked out the "big downhill" ones - its possible I missed a race or 2, I just picked out races I knew to have > Boston downhill.
REVEL Big Bear and Half Marathon (11/18/23 - Big Bear, CA) 1,837 742
REVEL Mt Charleston (4/1/23 - Las Vegas, NV) 1,516 555
St. George Marathon (10/7/23 - St. George, UT) 3,815 527
Mountains 2 Beach Marathon (5/21/23 - Ojai, CA) 1,423 401
Big Cottonwood Marathon (9/9/23 - Salt Lake City, UT) 1,572 335
Marathon P'tit Train du Nord (10/1/23 - Saint-Jerome, QC) 1,817 328
Light at the End of the Tunnel Marathon (6/11/23 - North Bend, WA) 757 297
The Tunnel Lite Marathon (9/10/23 - North Bend, WA) 664 226
Jack and Jill's Downhill Saturday Marathon (7/29/23 - Hyak to Tanner, WA) 761 175
Jack and Jill's Downhill Marathon (7/30/23 - Hyak to Tanner, WA) 510 156
Note that Marathon Guide mostly covers US/Canada, so I could be missing any big downhill races elsewhere.
Thats 3742 BQs, which assuming they all applied, would be ~11% of the applications for Boston 2024. How much would excluding those times move the needle? Realistically, I'd guess not more than a minute or so.
I suspect we'll see BAA to something eventually, because eliminating these races are an easy target to help lessen the cutoff. But I doubt BAA wants to be in the business of policing course profiles, and ultimately the general growth of the sport + super shoes means the times required to qualify are going to drop regardless.