When an appeal is transferred from one appeals court to another by the Supreme Court under Tex. Gov't Code 73.001, for which district is the resulting opinion controlling? My gut tells me the district from where the appeal was transferred, but I can find no authority for that....

TRAP 41.3 kind of addresses your question. Since the precedent of the transferring court court controls (if there is one), I would argue that the result you ask about controls in the transferring court.