Except then all games would lose support since none of them would run on ARM...so it'd be absolutely stupid for them to do so. Not to mention there are turns of mobile processors and GPUs that would work in a mobile handheld.
EDIT: OK FINE FOXI I'LL STOP POSTING IN THIS THREAD. FUCK.
Once again ninja'd by Foxi, no offense, I laughed really hard
Even if you port SteamOS to ARM (which would be silly), the game executables are for x86/x86_64, so it's counter-productive - none of the games would work without porting and recompiling them for the ARM distribution. I can guarantee you that this will be mobile x86_64.
You still don't get my point.
Let's suppose it will use something like Intel Atom, which is an x86 CPU,
even them, it won't magically make you able to use better CPU or RAM than the smartphones used nowadays.
You are still limited to mobile CPU and RAM, that will never compete with PC ones.