If visible precommitment by B requires it to share the source code for its successor AI, then it would also be giving up any hidden information it has. Essentially both sides have to be willing to share all information with each other, creating some sort of neutral arbitration about which side would have won and at what cost to the other. That basically means creating a merged superintelligence is necessary just to start the bargaining process, since they each have to prove to the other that the neutral arbiter will control all relevant resources to prevent cheating.
Realistically, there will be many cases where one side thinks its hidden information is sufficient to make the cost of conflict smaller than the costs associated with bargaining, especially given the potential for cheating.
If visible precommitment by B requires it to share the source code for its successor AI, then it would also be giving up any hidden information it has. Essentially both sides have to be willing to share all information with each other, creating some sort of neutral arbitration about which side would have won and at what cost to the other. That basically means creating a merged superintelligence is necessary just to start the bargaining process, since they each have to prove to the other that the neutral arbiter will control all relevant resources to prevent cheating.
Realistically, there will be many cases where one side thinks its hidden information is sufficient to make the cost of conflict smaller than the costs associated with bargaining, especially given the potential for cheating.