I created a branch quite a while back with a few features to help with creating repeating textures/terrains. It didn’t quite make sense at the time, and there were a few significant issues holding it back.
However especially with Artist Point here, being able to create your own texture assets within a world/macro is pretty useful, and of course they need to tile to do that…
There’s a featureupvote entry for this request: Ability to create repeating (tiling) textures - World Machine