It makes little to no difference where the Hopper is located. I specifically asked this (in another thread). The only reasons given (granted, there can be more) were: 1) Loss of PIP/SWAP and 2) noise.
What would you lose by having the Hopper not on your main TV ?
Depends how you look at it - developing the main system, i.e. a 4K Hopper, would certainly take a lot longer than a 4K Joey. I guarantee you, Dish is working on a 4K Hopper right now. No, I'm not a Dish employee and no, no one from Dish told me this, but I know enough about engineering/design, manufacturing, etc to realize that they'd better be !