My request is for a mechanism to force load cells in World Partition. Terrain cells are not actors, and cannot be placed on data layers (to the best of my knowledge).
I tagged this as crash, as this is exactly what happens in my use case. I implemented portals (as actors), and it is reasonable to have these portals far apart. On a large outdoor terrain, a portal might be in a cell which is far from the player and thus not loaded. I have seen game crashes with assertion failures related to terrain not being loaded.
The only change I think is needed is to give us a way (hopefully in Blueprint as well) to force load a particular area of the world. Not a suggestion to load it, but a way to compel World Partition to load the terrain. With my portals it would be easy enough to have a collision volume near a portal which will trigger the loading of the area containing the paired portal. Or all cells with portals could be loaded when the level loads. But watching the game crash is a sad thing. Suggesting terrain should be loaded, or prioritizing it, are both a bit less than my desired solution.