I want to make it clear that it is just a rumor, but if it is true, it would be a huge breakthrough in Microsoft policy. Michael Larabel, author of the blog Phoronix, which has repeatedly been accused of making things up, reports that Microsoft is considering making Office for Linux. I do realize that it may sound unbelievable, but keep in mind that the same author reported about the Steam client for Linux (which turns out to be true).
The source of this news comes from the FOSDEM (Free Open-Source Developers' European Meeting) in Brussels. Michael was one of the guests and during the meeting, he got informed that Microsoft is seriously considering moving to Linux Office, due to the increasing number of pc's with Linux.
Currently, the only way to use Office on Linux, is to run the 2010 version in Wine - win32 libraries implementation for Unix-like systems. This solution, however, has no value for a business usage. No one does guarantee the stability of the application and there is not technical support provided.
Many people have doubts that Linux scenario for Microsoft Office is possible. Skeptics should be remember that Microsoft is planning to release Android and iOS version of Office, which was reported by The Verge. Releasing a Linux edition on the desktop, at first glance seems to be a mistake: what about the sales of Windows, boosted by the need to run Office? In the case of OS X you could even justify it by the popularity and the cost of mac's machines - hardly anyone will spend few thousands dollars for a secretaries workstation. Linux, however, can be easily run on almost any PC, so in many cases purchasing a Windows license would not make sense.
On the other hand, however, it may be that maintaining a long term monopoly on office software, is for Microsoft more important, than a monopoly in the operating systems market(which is not as significant as it was in the 90's). In a situation where more and more public institutions around the world decided to migrate to Linux desktops, and as a result, migrate to LibreOffice or OpenOffice, the availability of the standard - from a business perspective - Microsoft Office, could effectively stop the weakening of the position of Word, Excel and PowerPoint.