Not sure what would be the purpose of that, seems like a bit too much work for Valve themselves to port games to Linux when the developers don't bother doing so.
Not sure how Linux = Android because it doesn't. Most Android apps run through the Dalvik VM which is basically Java, even the native code API's are different.
A Steam store for Android might work but it's hard to say, iOS would obviously be out of the picture.
I say go for it Valve. Lots of people use Linux and have been left out of the gaming segment and they need to use tools like Wine, etc to get games to work on Linux and they don't always work that great if at all.
So having a big company with an easy to use platform for installing games that WORK on Linux would be great and probably quite profitable for Valve's monster distro platform.