ὁ ἐρχόμενος could merely be saying that God will continue to be in the future but if taken as "will be coming in the future" then we see that graphically described in chapter 21.
The traditional hope of the Christian is to "go to heaven" but the scriptural hope has always been to live with God in the promised land:
Rev 21:2 And I John saw the holy city, new Jerusalem, coming down
from God out of heaven, prepared as a bride adorned for her husband.
Rev 21:3 And I heard a great voice out of heaven saying, Behold, the
tabernacle of God is with men, and he will dwell with them, and they
shall be his people, and God himself shall be with them, and be their
Hence the prayer "Thy kingdom come". And:
Heb 11:8 By faith Abraham, when he was called to go out into a place
which he should after receive for an inheritance, obeyed; and he went
out, not knowing whither he went. Heb 11:9 By faith he sojourned in
the land of promise, as in a strange country, dwelling in tabernacles
with Isaac and Jacob, the heirs with him of the same promise: Heb
11:10 For he looked for a city which hath foundations, whose builder
and maker is God.
So the description of God's dwelling place descending shows that God is going lives in a mobile home which he will relocate to his sacred property in the middle east. This is him "coming".
Mic_4:7 And I will make her that halted a remnant, and her that was
cast far off a strong nation: and the LORD shall reign over them in
mount Zion from henceforth, even for ever.
Isa 24:23 Then the moon shall be confounded, and the sun ashamed,
when the LORD of hosts shall reign in mount Zion, and in Jerusalem,
and before his ancients gloriously.
The synopsis/Cliff Notes version of the Revelation is this:
- divine terrorism poured out from the sky will demoralize the nations
- Jesus will gather the saints to the middle east and reign for a thousand years
- Jesus will step down and become just another Joe and God himself will descend from the sky and rule alone forever
In this way God is the one who is coming.
For an even shorter synopsis of the Revelation:
1Co 15:24 Then cometh the end, when he shall have delivered up the
kingdom to God, even the Father; when he shall have put down all rule
and all authority and power.