Who are the subjects in the new heavens and earths if according to Rev 1:6, 5:10, 1 Peter 2:9, everyone is made a king. Thanks
I think it best to understand this language of king and priest in the context of Christ and our being Christ-like, not in a context of hierarchy over others. The hierarchy being applied is couched in the Dominion or Cultural Mandate of Gensis 1:26-28.
Genesis 1:28
God blessed them; and God said to them, "Be fruitful and multiply, and fill the earth, and subdue it; and rule over the fish of the sea and over the birds of the sky and over every living thing that moves on the earth."
That's the first command/blessing God ever bestowed upon humanity and it's been reasserted and rephrased numerous times in scripture, but never revoked. It was given in the pre-disobedient creation so it should not be understood as solely applying to the post-disobedient sinfully sin-filled world. When God first began speaking a about a "nation" or "kingdom" to the Hebrews He did so saying,
Exodus 19:1-6
In the third month after the sons of Israel had gone out of the land of Egypt, on that very day they came into the wilderness of Sinai. When they set out from Rephidim, they came to the wilderness of Sinai and camped in the wilderness; and there Israel camped in front of the mountain. Moses went up to God, and the LORD called to him from the mountain, saying, "Thus you shall say to the house of Jacob and tell the sons of Israel: 'You yourselves have seen what I did to the Egyptians, and how I bore you on eagles' wings, and brought you to Myself. 'Now then, if you will indeed obey My voice and keep My covenant, then you shall be My own possession among all the peoples, for all the earth is Mine; and you shall be to Me a kingdom of priests and a holy nation.' These are the words that you shall speak to the sons of Israel."
And, of course, contrary to Dispensationalist views, Peter tells us this is an already-inaugurated condition.
1 Peter 2:9-10
But you are a chosen race, a royal priesthood, a holy nation, a people for God's own possession, so that you may proclaim the excellencies of Him who has called you out of darkness into His marvelous light; for you once were not a people, but now you are the people of God; you had NOT RECEIVED MERCY, but now you have received mercy.
It helps to understand,
from God's perspective, the proper understanding is NOT to divide the priest from the king. Adam (and Eve) were the sovereigns of the earth; bestowed by God with all the power and authority, and good, unashamed, and sinless disposition, to accomplish the task of ruling multiplying, subduing, and ruling. We first see this unified ontology in Melchizedek, the king AND priest of Salem, the city of peace (jeru = city, salem = peace). We first see the roles divided at the burning bush when Moses balks at God's command to be His representative before Pharaoh AND leader of the soon-to-be-liberated Hebrews. Moses debates (defies) God, God acquiesces, and the result is Moses speaking for God and Aaron speaking for Moses, the two eventually becoming the civil and religious rule divided. Later, in the case of the Judges, God reinstitutes the unified rule but sinful man is imperfect and the Judges failings prompt the Jews to request and earthly king like all the other nations, which is something God explicitly repudiates and openly takes as a rejection of Himself as King.
There has always been only one King.
There has NEVER been a fraction of a moment in all of creation when God is not sovereign over all.
There have been plenty of occasions when humans, including God's own people, have not perceived that truth and settled for second-best.
ALL of scripture testifies to and about Christ and Christ is King and Priest. Not an Aaronic priest, but a Melchizedekian Priest; that of a much higher order than the temporal version for which Moses (and the rest) settled. We, the regenerate believers, have and are being made in the image of
that Guy. All humans bear the image of God asserted in Genesis 1:26, but
we bear the additional image of that found in the resurrected Son, and it the purpose of the Church to make sure that is manifest.
Ephesians 4:11-16
And He gave some as apostles, and some as prophets, and some as evangelists, and some as pastors and teachers, for the equipping of the saints for the work of service, to the building up of the body of Christ; until we all attain to the unity of the faith, and of the knowledge of the Son of God, to a mature man, to the measure of the stature which belongs to the fullness of Christ. As a result, we are no longer to be children, tossed here and there by waves and carried about by every wind of doctrine, by the trickery of men, by craftiness in deceitful scheming; but speaking the truth in love, we are to grow up in all aspects into Him who is the head, even Christ, from whom the whole body, being fitted and held together by what every joint supplies, according to the proper working of each individual part, causes the growth of the body for the building up of itself in love.
Lastly part of the answer to this op's inquiry is found in verses like 1 Corinthians 6:3,
1 Corinthians 6:3
Do you not know that we will judge angels? How much more matters of this life?
No other creature is made in God's image. No other creature is offered salvation from sin and wrath. We're the Judge's judges

. Who knows what tasks lay beyond the resurrection for those made in His image to whom alone grace has been showed?