I'm planning on a circular world border with a radius of 100k. Currently there are only 52 players that are further than this distance from spawn. To calculate your distance, you need to compute the square root of your coordinates squared:
distance = sqrt(x*x + z*z)
I'll be reaching out to these specific players later on, but I wanted to give you guys a heads up now on what I'm planning.
I plan on enabling the world border (and pushing any players back closer to spawn) a week from now, Sunday June 9.
Then I'll follow up with the 1.14.2 update shortly thereafter assuming everything goes well and enough space is recovered.