As a Roblox developer, it is currently impossible to tell streaming to stream out models that aren’t near the player. This would be nice because Roblox ends up networking a lot of changes that aren’t local to the player on join.
For example. these bird wings are moving even though the player can’t see them:
I move them into the primary part, and now they aren’t replicating. 
I would also like attachments underneath terrain to not replicate when the player is near them, and nothing replicated to the player is close. I understand this may be harder to do.
Basicaly, I want these models underneath to not be replicated to the client. This will have good performance benefits in my game. Especially given potentially nested models like this:
Nothing in this model is replicated, so I"d much rather just have the whole model gone.
If Roblox is able to address this issue, it would improve my development experience because my game wouldn’t replicate a lot of unnecessary constraints to the client.
This needs to be an option, I think some people rely upon the hierarchy like this replicating, but I’d like to not do that. My game is programmed to not assume the existence of anything past terrain and current camera in workspace.