Ah, interesting points
You should read John Chrysostom’s homily on this though:
See
newadvent.org/fathers/220140.htm
Homilies on First Corinthians (by John Chrysostom) (347-407 AD)
I’m still going to meditate on this further, but at this point in time I’m not sure if I could subscribe to your interpretation fully since Paul seems to be referring to the sacrament of Baptism. I say this because he is talking about Christ’s resurrection. It isn’t quite making sense to me why he would suddenly throw in suffrage for the dead when he is talking about Christ’s resurrection, and their faith, which they professed at Baptism. I would very much like to see more New Testament support for prayers for the dead (not that I need that to prove it; history proves it), but I don’t think this is a very strong case for it.
Paul calls baptism a burial, saying, “Therefore we are buried with Him by baptism into death.” in Romans 6:4, and throughout Roman’s 6 he uses the same language when talking about the Sacrament of Baptism.
Keep in mind that the blotting out sins is a much greater thing than the raising up of a body. Christ declared this when he said, "It is easier to say, Your sins are forgiven, or to say, Take up your bed, and walk? (Matthew 9:5). To say ‘your sins are forgiven’ is the more difficult, but since they didn’t believe Him, he demonstrated how easy it was for the body to rise by saying, “Arise, take up your bed, and go to your house.”.
It seems more likely that Paul is asking a rhetorical question of sorts. In other words: What are you going to do since you were baptized for the dead (not into life-- see Romans 6)? If you believe there is no resurrection, then why are you baptized for the dead (what’s the point)? To me that is what he is saying, and this is in harmony with Romans 6 and, well, everything else in the gospels.
“But he said to another: Follow me. And he said: Lord, suffer me first to go, and to bury my father. And Jesus said to him: Let the dead bury their dead: but go thou, and preach the kingdom of God.” Luke 9:59-60
Paul’s reasoning in 1 Corr 15 follows this teaching: those who do not believe in the resurrection are spiritually dead, and, therefore, they were baptized for the dead, not into life.
Furthermore, if we do not interpret verse 29 in that manner, then what do we make of Paul’s command “Let us eat and drink, for tomorrow we shall die.”? It seems to me (at this point) more likely that Paul is simply being rhetorical rather than referring to the prayers for the dead.
I realize Challoner, in his commentary, states exactly what you are saying, but he puts it forth as a suggested interpretation, not as an infallible one.