I've been doing a little reading around, and here is another angle, one that I think makes a decent amount of sense. To understand it, we should pull up the larger context of the passage in discussion.
1 Peter 3.18-22: For Christ also suffered once for sins, the righteous for the unrighteous, that he might bring us to God, being put to death in the flesh but made alive in the spirit, in which he went and proclaimed to the spirits in prison, because they formerly did not obey, when God's patience waited in the days of Noah, while the ark was being prepared, in which a few, that is, eight persons, were brought safely through water. Baptism, which corresponds to this, now saves you, not as a removal of dirt from the body but as an appeal to God for a good conscience, through the resurrection of Jesus Christ, who has gone into heaven and is at the right hand of God, with angels, authorities, and powers having been subjected to him.When reading this, we see that Peter is speaking about Christ, but then, for some reason, in the middle of his teaching of Christ he interjects a thought about Noah and the flood. Basically, it appears that verses 3.19-21 are a digression; Peter is speaking about Christ in verse 3.18, but then adds in a sort of parenthetical thought, and returns to speaking about Christ in 3.22. What does the text look like, if we momentarily pass over verses 3.19-21?
1 Peter 3.18,22: For Christ also suffered once for sins, the righteous for the unrighteous, that he might bring us to God, being put to death in the flesh but made alive in the spirit, ... who has gone into heaven and is at the right hand of God, with angels, authorities, and powers having been subjected to him.What we are left with is a continuous, uninterrupted description of Christ's death, resurrection, and ascension. It is quite similar to certain "creedal" passages found in Paul's epistles. [Romans 1.3-4; 1 Corinthians 15.3-5; Philippians 2.8-10; 1 Timothy 3.16; which, as noted before, were other passages that used "the flesh" and "the spirit" as parallel statements to refer to Christ's earthly body and his resurrection] In this understanding, verses 3.19-21 a parenthetical thought Peter had when describing Christ's death, resurrection, and ascension. Hence, verses 3.19-21 would not be part of the chronology of events Peter describes in 3.18,22. Peter mentioned Christ's resurrection, "made alive in the spirit", and was struck with an additional thought, which he jotted down. Then, after finishing this thought, he continued to describe Christ, "who has gone into heaven..."