My guess is that if HA and AS merge their loyalty program into MP, there will be a period of time where transfers from Bilt -> HA becomes Bilt -> AS, assuming HA's contract runs through the date the combined loyalty program is MP.

I would question whether or not AS renews it though. It was a bit different having AA join in 2021 when Bilt's card issuer was through some rando fintech firm affiliation with Evolve Bank (I actually have this card, not the WF card) as opposed to Wells Fargo, which is very obviously a direct competitor to BofA and Citi (and is implementing transferrable points that have some overlap with Bilt).

FWIW though... AF/KL issue cards through Bank of America like AS does, and they also partner with EVERYONE in the transferrable miles space: AMEX, Chase, Capital One, Citi, Bilt, Wells Fargo. So maybe BofA won't care. Maybe AS won't care if they lose some control of their mileage minting (I suspect they view BofA not having transferrable miles as a feature, not a bug, it helps with controlling the program).