Quite a few religions will regard the present moment as such (Buddhism, Judaism), but not all propose an afterlife. Whether all the world is the Kingdom, by definition Heaven is too.
The weight of messaging and interpretation shifts with the times to capitalize on the fact that people are more life-affirming when times are good, and if broadly there's toil and suffering, well, hope for peace in the next life.
I think it's disingenuous to ignore the distinction. You can quibble about what-its-all-about, but in accordance with the dogma there's either afterlife or there isn't, and that knowledge is so prominent in popular culture that non-believers know it, people from other cultures know it.
My perspective strongly identifies the phrase "the kingdom of god" with Isaiah's vision of the mountain, which is firmly of this world and our time. It is a making-right of this world that we should never forget to strive for.
The mistake that rather a lot of my evangelical cousins make (i am not one) is that, to paraphrase James, they tend to be so focused on the life to come and have such a crabbed interpretation of "staying unblemished by the world" that they entirely forget -- or worse, regard as something that blemishes you -- the "visiting the widows and orphans in their distress" clause. And that just won't do.
