Android used to support MIPS and x86_64 - in fact I think it still supports the latter. Of course, that might just mean that Google is painfully aware of how annoying that is to handle:)
They do, as well as x86 (32-bit); they are targets for emulator system images.
Not only that, there were some x86-based (but not PC-BIOS) devices running Android out of the box.