One of the iFixit Valve Stream Machine prototype is over the web, this gaming Stream Machine is completely upgradable.
The entire parts of this Stream Machine includes powerfull 3.2GHz ( turbo at 3.6GHz ) quad-core Intel Haswell Core i5-4570 processor, 16GB of RAM, a Zotac GeForce GTX 780 graphic card with 3GB GDDR5 VRAM and a 1TB ( Terabyte ) Seagate SSHD ( Solid State Hybrid Drive ). If you think to build your own Stream Machine with above given parts then it would cost you around $1300.
The entire part of Stream Machine is designed to be opened with removal of single Phillips screw. Once Stream box upper case is removed, the SSH drive and GTX 780 graphics card seem easily replaceable. The RAM and motherboard requires to remove plastic cowl as motherboard is a ASRock Mini-ITX Z87E, its easy to replace or upgrade motherboard, CPU, RAM and cooler.
Not only these thing Stream Machine have. There you find 450W 80 plus Gold PSU and a fancy logic board having 12 LEDs. In case of repairability, iFixit gives 9 out of 10 score. Losing 1 score point for difficult to remove motherboard cowling and precise cable routing during repairing or upgrading.