Well, you can't stand out by just following what big companies are capable to offer better.
Valve's job to improve Linux's driver will come to benefit to everyone (that's the greatness of the open source), and any Linux derivative. On the opensource side is even better with Intel/AMD graphic stack... which mean that driver can be delivered to work out-of-box, at full performance, without infringing licensing issues with GNU.
Anyway, having an ItchOS doesn't mean that the main app couldn't work into steam as non-steam app.
The capability to boot your own complete gaming platform on something simple like a usb dongle, it's an added value/capability that Steam doesn't have.