I believe it's the file system (HFS/HFS+?) that has the 4TB Limit. It would be interesting to see what the next version of File system apple is gonna come out with if HFS+ limit ever gets released. I am thinking they would go with eFS if anything. (I think I did that right. It might be ExtFS+ or something)

But yeah, t'would be intersting to see what comes out. Maybe ZFS?