Is this even physically possible, given the worldwide birth rate?
I don’t know how much we can do but it may be possible for nations to open up to missionary work and when they do, it will be incumbent upon Christians to set up churches in those nations. I don’t see it meaning every single person should hear the gospel, but I think they need to have the means to do so if they hear about it and are wondering. Right now, I don’t think that exists, even with the internet.
You said — “Is this even physically possible, given the worldwide birth rate?”
Yes, it’s possible when you have an angel circling the globe, giving everyone the message of the Gospel of Jesus Christ...