The best way to understand what Peter is doing in 1 Peter 4:6 is to study 1 Peter 4:6 in context. Let's start by trying to get the gist of what Peter was attempting to communicate in the passage.
1. Review the author's flow of thought
The flow of thought in the context containing this verse (4:1-7) is as follows:
Just as Christ suffered death in His flesh, you likewise should die to your flesh, because he who has died to his flesh has turned from a life of fleshly sin to a life lived for the will of God. (4:1-2)
You used to live sinful lives like the Gentiles do, and now that you don't, they are all astonished. But they will give an account to God, who is ready to judge both the living and the dead (v.3-5)
...which, incidentally, is why the gospel has been preached even to those who are dead: so that even though they are judged in the flesh (because they are men), they may live in the spirit (because of the will of God) (6)
The end of all [fleshly] things is near, so live like it . . . (v.7ff)
2. Determine the function of the verse in question
In reviewing the author's flow of thought we see that the verse in question follows on the heels of a statement about God being ready to judge both the living and the dead. So both the living and the dead will answer to God for their lives some day. Then he explains that this is why the gospel was even preached to those who are now dead, so that even though God is going to judge everyone -- living and dead -- the dead who embraced the gospel (i.e. while they were alive) could have spiritual life despite their physical death.
3. What is Peter referring to in 4:6?
Peter's audience of late-century Christians undoubtedly knew people who had embraced the gospel and then died. These Christians were now facing death themselves. Peter is explaining in his exhortation to these Christians that everyone is going to die, but those who die to the flesh to follow Christ will live forever, despite their physical death. That is the whole reason the gospel was preached to them while they were still alive! So Peter's letter helps his audience to persevere in the gospel.
Is this an "eternity perspective"
Probably not. Peter seems to be explaining something to his audience about the people they were familiar with who had died after embracing the gospel. He seems to be exhorting them not to lose heart, but to persevere in following Christ, despite their certain death. This fits perfectly with themes that run throughout the rest of his letter (and, in fact, the rest of the New Testament.)
