Is Paul's singling out of 3 specific spiritual gifts (prophecies, tongues, knowledge) in 1 Cor 13:8 intentional or rhetorical?
It seems that this is more intentional on Paul's part. Let's look at some of the evidence to this.
The subheading "Miraculous powers" in the topic "Apostle" from the *Insight on the Scriptures" notes the following:
Additionally, to fortify their testimony, the apostles continued to exercise the miraculous powers previously granted them by Jesus, and also other gifts of the spirit received from Pentecost forward. (Ac 5:12; 9:36-40; see GIFTS FROM GOD [Gifts of the Spirit].) While others, too, received such miraculous gifts of the spirit, the account shows that such was the case only when one or more of the apostles were present, or by the laying on of the hands of the apostles. Paul, though not one of the 12, also served in this way as an apostle personally appointed by Jesus Christ. (Ac 2:1, 4, 14; 8:14-18; 10:44; 19:6) Thus the power to transmit such gifts was unique with these apostles. Such miraculous gifts would therefore pass away with the passing away of these apostles and of those who had received these gifts through the apostles (1Co 13:2, 8-11), and thus we read that these powers were “missing in the 2nd-century church, the writers of those days speaking of them as a thing in the past—in the apostolic age, in fact.”—The Illustrated Bible Dictionary, edited by J. D. Douglas, 1980, Vol. 1, p. 79. [bold mine]
This is supported further in the topic "Power, Powerful Works" of the *Insight on the Scriptures:
It was foretold that miraculous abilities granted by the spirit to the apostles, and passed on by them to others, would last only during the ‘infancy’ of the Christian congregation, thereafter ending. (1Co 13:8-11; see GIFTS FROM GOD [Gifts of the Spirit].) M’Clintock and Strong’s Cyclopædia (Vol. VI, p. 320) says that it is “an uncontested statement that during the first hundred years after the death of the apostles we hear little or nothing of the working of miracles by the early Christians.” Nevertheless, Jesus and his apostles warned of future deceptive powerful works that would be done by apostates and also by a symbolic wild beast, enemies of God.—Mt 7:21-23; 24:23-25; 2Th 2:9, 10; Re 13:11-13; see BEASTS, SYMBOLIC. [bold mine]
The original Greek also supports this. In the Reasoning From the Scriptures, the topic "Tongues, Speaking in" has the question "Is ‘speaking in tongues’ to continue until that which is “perfect” comes?"
At 1 Corinthians 13:8 reference is made to several miraculous gifts—prophecy, tongues, and knowledge. Verse 9 again refers to two of these gifts—knowledge and prophecy—saying: “For we know in part, and we prophesy in part.” (KJ) Or, as RS reads: “For our knowledge is imperfect and our prophecy is imperfect.” Then verse 10 states: “But when that which is perfect is come, then that which is in part shall be done away.” (KJ) The word “perfect” is translated from the Greek teʹlei·on, which conveys the thought of being full grown, complete, or perfect. Ro, By, and NW here render it “complete.” Notice that it is not the gift of tongues that is said to be “imperfect,” “in part,” or partial. That is said of “prophecy” and “knowledge.” In other words, even with those miraculous gifts, the early Christians had only an imperfect or partial understanding of God’s purpose. But when the prophecies would come to fulfillment, when God’s purpose would be accomplished, then “that which is perfect,” or complete, would come. So, this is obviously not discussing how long the ‘gift of tongues’ would continue.
However, the Bible does indicate how long the ‘gift of tongues’ would be a part of Christian experience. According to the record, this gift and the other gifts of the spirit were always conveyed to persons by the laying on of hands of the apostles of Jesus Christ or in their presence. (Acts 2:4, 14, 17; 10:44-46; 19:6; see also Acts 8:14-18.) Thus, after their death and when the individuals who in that way had received the gifts died, the miraculous gifts resulting from the operation of God’s spirit must have come to their end. Such a view agrees with the purpose of those gifts as stated at Hebrews 2:2-4.
We can also see that Paul is making a contrast of these three spiritual gifts in contrast with love of which Paul states "Love never ends." If the spiritual gifts were to continue, why would Paul contrast them with love's neverending quality?
So, yes, Paul was speaking of these spiritual gifts intentionally and not rhetorically.
[All scripture quotations from the New World Translation of the Holy Scriptures (Study Edition)]