I remember there being some speculation way back (maybe in the Oathbringer days?) where we knew there were 3 Bondsmith Spren but didn’t know about The Sibling at the time. I remember there being a little theorizing that the third would be BAM. With 3 shards on the planet, it makes some sense that each one would have one Spren that’s the biggest one that can form a Bondsmith.
This was deconfirmed in ROW not only because we found out about The Sibling, but also because we learned that adhesion is “Honor’s truest surge” and so it couldn’t be accessed by Odium. With that knowledge, even if BAM formed a radiant bond, it wouldn’t create a Bondsmith, because she’s a spren made of Odious investiture. But now that we have WaT it feels like the theory might have legs again. Let me lay out the supporting evidence.
1) With Odium becoming Retribution, it makes sense that he and his spren would be able to access Honor’s surge
2) Mishram already has pulled Connection shenanigans in the past, when she Connected to all the singers
3) As an unmade she is presumably formed from corrupted investiture so she could still have a lot of Honor in her, if she was a Spren made of Honor stuff before being unmade. (Although she could easily also be an Adonalsium Spren like the Wind)
4) She is unlikely to be working on Odium’s side in future books, considering how scared Rayse was of her taking the power from him. I could easily see her being a candidate to hold Retribution as well. It seems entirely possible that she might form a Radiant bond as part of her action against Retribution.
5) Spren created Radiants independent of Honor originally. There’s no reason Retribution should be able to stop BAM from doing this.
6) Thematically, I think it works for her story arc. She originally was trying to “bring humans and singers together” in a sense by ending the war. She saw two lovers, one singer and one human, that led her to be trapped, and then eventually was freed by another pair of lovers, one singer and one human. She was trapped by connections thematically, and then freed by them.
7) Seeing a singer Bondsmith bonded to BAM would be a pretty crazy reveal and could work really well as a climactic moment in a future book.