1 Pet.4:2,5-7  That he no longer should live the rest of his time in the flesh to the lusts of men, but to the will of God... Who shall give account to him that is ready to judge the quick and the dead. For for this cause was the gospel preached also to them that are dead, that they might be judged according to men in the flesh, but live according to God in the spirit. But the end of all things is at hand: be ye therefore sober, and watch unto prayer.

 

It looks like 1 Pet. 4:4-6 might have 2 possible interpretations, the gospel being preached to them that are physically dead or spiritually dead. If it is physically dead (which may be indicated by v5) then it could match up with the Old Testament saints (Rom.3:25, Heb.9:15) in Abraham's bosom (Lk.16:19-31) and Christ preaching the gospel to them at his death and descending first into the lower parts of the earth (Eph.4:8-10). In this case they will be judged according to deeds done in the body (2 Cor.5:10) as men living in the flesh (v2, Gal.2:20) and live in a resurrected spiritual body (1 Cor.15:44).
If it means spiritual dead (Eph.2:1) then the gospel "preached to every creature under heaven" (Col.1:23, as in once delivered Jd.3) was so while they will be judged according to deeds done in the body (2 Cor.5:10) as men living in the flesh (v2, Gal.2:20) they could live in the Spirit (Rom.8:13). (Or if he means the spirit of man by the lower case 'S' which wouldn't have to be so necessarily- Ezk. 36:27, 37:14, Mt.22:43, Mk. 12:36, then it might be in newness of the spirit as in Rom.7:6.)
It seems like the latter makes more sense in context because he "is ready to judge" (his coming- 2 Tim.4:1) and "the end of all things is at hand", so "for this cause" (we persuade men- 2 Cor. 5:10-11) was the gospel preached to every creature. v2 That he no longer should live the rest of his time in the flesh (that is according to men in the flesh) to the lusts of men, but to the will of God- that is, live according to God in the spirit. So they might be judged according to men in the flesh, but also live according to God in the spirit. In other words, The gospel was preached to the lost, so that although they are judged according to men in the flesh in the day of judgment for deeds done while in the body, they can live according to the will of God in the Spirit in this life. And, the gospel was preached also to them that are dead, not were dead. This would agree with the latter explanation.

And further, we see the imminence of Jesus return that Peter is expressing in v7 also in v5 when he declares Christ is “ready to judge the quick and the dead” making reference to the Gentiles in their sin (v3-4). To this agrees James 5:8 “the coming of the Lord draweth nigh” and v9 “the judge standeth before the door”. Peter also expresses this in 2 Pet.3:10 “the day of the Lord will come as a thief in the night”. When the Judge comes in that millennial day (see #1 here) the righteous will be judged first (1 Pet.4:17-8) at the beginning of the day and the wicked judged at the end of the day. (Rev.20, 2 Pt.3:7-12) The wicked will be killed in the beginning of that day only to rise again and “give account” (v5, Mt.12:36, Rom.14:12) in the resurrection of shame and everlasting contempt at the end of that 1000-year day. The resurrection of the just and the unjust (Jn.5:29, Dan.12:2, Ac.24:15, Rv.20:4-6) are separated by 1000 years but are spoken of as occurring "in the last day". (Rev.20:4,5:11-12, Jn.6:39-40, 44, 54, 11:24, 12:48, 5:28-9) When scripture says “one day is with the Lord as a thousand years, and a thousand years as one day” (2 Pt.3:8, Psa.90:4) it also describes 'the' thousand-year period of time with 6 references in Rev.20:1-7.