While technically an irrevocable promise, in practice the OSP is good only for today.
On the back of a chaotic ISO meeting to resolve outstanding specification problems which was described as "Complete, utter, unadulterated bullshit. This was horrible, egregious, process abuse and ISO should hang their heads in shame for allowing it to happen." by Tim Bray, this advice throws more doubt on OOXML's suitability as an international document standard.
Despite these considerable doubts, countries like Australia and New Zealand have not committed their votes, and it's still not clear how the race will run at the March 29 deadline.