I doubt they have that much resources to spare. Also when competing with free software, MS probably will just advice using SkyDrive. If it is really desired, I would rather make an Android version.
That's true. Office 365 is already cross-platform and will work on Linux (although it being Microsoft, not free, not open source and holding documents in the cloud, I suspect a fair number of Linux users would rather poke their own eyes out with a spork first).
The bit I don't understand is what the commercial driver for the Office team messing about with Linux would be. Porting Office to Linux is a lot of work (read: expensive), and the market of people on Linux who really want to spend real money on Office to run on their Linux desktop who don't already use OO, Libre, Office in a VM or Office on WINE sounds to me like a really tiny number of people.