Paul never referred to his letters as new books of Scripture, nor did he ever describe anyone else's writings as being new books of Scripture. Certainly Paul's letters are inspired Scripture, but the point is that Paul never made any kind of reference to a "New Testament" or a new set of Scriptures. We have no Scriptural evidence for taking Paul's vague statement, "when perfection comes, the imperfect disappears," as being a reference to the completed New Testament because Paul never mentioned such a thing as a "New Testament." In fact, after Paul died, roughly 75 years went by before anyone even tried to formally put together a new set of Scriptures, which we now call "the New Testament" (The History of Christianity, Dr. Tim Dowley, p.106)(There is another reference for you DHK!). This makes it even less likely that Paul had such a thing in mind in 1 Corinthians 13:10.
2 Peter 3:15 And account
that the longsuffering of our Lord
is salvation; even as
our beloved brother Paul also according to the wisdom given unto him hath written unto you;
16 As also in
all his epistles, speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest, as
they do also the other scriptures, unto their own destruction.
--Peter considered the epistles of Paul as Scripture, and apparently knew which ones were and which ones were not. I say that because Paul wrote 4 epistles to the Corinthians, and only two were inspired, but Peter knew which ones they were.
1 Corinthians 7:10 And unto the married I command,
yet not I, but the Lord, Let not the wife depart from
her husband:
--This is a claim to inspiration. Paul is saying that these words are not his but the Lord's.
1 Corinthians 11:23 For I have received of the Lord that which also I delivered unto you, That the Lord Jesus the
same night in which he was betrayed took bread:
24 And when he had given thanks, he brake
it, and said, Take, eat: this is my body, which is broken for you: this do in remembrance of me.
25 After the same manner also
he took the cup, when he had supped, saying, This cup is the new testament in my blood: this do ye, as oft as ye drink
it, in remembrance of me.
26 For as often as ye eat this bread, and drink this cup, ye do shew the Lord's death till he come.
--Paul was never in the upper room with the disciples.
And yet he quotes the exact words of Jesus and what happened there. How did he know? These are the words of the Lord, Scripture. They are the inspired words of God.
Or, are you an unbeliever and don't believe the inspired word of God?
Your theory implies that the Apostles were dumb and stupid and not intelligent enough to teach the early church which of their writings were inspired and which were not. They had the completed canon of Scripture by the time John wrote Revelation. They had the books as they were written. It is evident that at the time of Peter, he knew which of Paul's epistles were Scripture, and refers to them as such.