i could see valve making a new steam console with upgraded hardware every year... and giving a big discount to people already owning the console
it would be almost as what happens in pc... you buy hardware, when you want to upgrade, you sell the part and buy the new part.
But as valve probably wouldnt get any money from part upgrades, they would sell you the console again and "buy" the old console back. Then they would just open it, take out the outdated part, insert the new one and sell it again
seems like a cheap and easy way to upgrade your hardware all the time instead of limiting the games to your hardware that wont be upgraded for a long long time