I think it is possible that future iPhone and Samsung Galaxy S phones in the near future like iPhone 8 and Samsung Galaxy S8 will have 500GB or more storage for the most expensive version of an unlocked iPhone and Samsung Galaxy S phone. The iPhone 7 already has 256GB of storage when you buy the $1000 iPhone 7 256GB.
There are already SD cards which has 500GB of storage, and I read recently that there is a 1TB SD card which is not released yet, so there are memory storage chips which can store 500GB to 1TB of storage.
I agree, I would rather have 1TB since it is more space. I feel 500GB is not much space for playing a lot of emulators, and larger games on a phone or tablet because games need to be physically stored on the storage drive instead of running off a disc or cartridge like the Playstation and Playstation 2, or the Xbox 360 which let you play most games off a disc without installing them on the hard drive.
