sorry for being offlanguage:
in another game engine I use sometimes treadmill is a built-in feature. there you have world elements called areas, and every static object corresponds to an area, areas also have navmesh data for pathfinding. they are streamed in the background as the character moves around. an area size is relatively small, like one terrain chunk size in 3DGS, 32x32 vertices which can be 31x31m if you use a 1x1m terrain resolution (which is high). for higher FOV far areas are assigned as passive ones, and only rendered without AI calculations. their loading is kept relatively unnoticable, what I don't know how can be done in 3DGS, but hopefully possible.