There's not much to see, since it's in the menu before you join the game, but here you go. Nowhere in the UI (including in mouseover tooltips) is there any indicator of how many players are on the realm:
There's not much to see, since it's in the menu before you join the game, but here you go. Nowhere in the UI (including in mouseover tooltips) is there any indicator of how many players are on the realm: