Ultimately standard compliance is only a means to an end. The end most organisations are looking for when they ask for standard compliance is the avoidance of vendor lock-in. Thus far those organisations simply *assumed* and trusted that standard compliance was adequate to avoid vendor lock-in.

At this point, it would seem that with OOXML becoming an ISO standard, the underlying assumption that standard compliance alone is adequate to avoid vendor lock-in will no longer hold true. If so, then organisations whose goal it is to avoid vendor lock-in will very likely adjust their procurement rules and update the requirements accordingly.

A very simple workaround would be something like this:

"Any software to be procured must conform to the applicable ISO standard. In the event that there are multiple applicable ISO standards, any software to be procured must conform to at least one applicable ISO standard for which conforming applications from multiple competing vendors are available."

After all, that has been the true objective all along, not buzzword compliance. If the buzzword doesn't meet the objective any longer, simply write the objective plain and clear into your requirements, very simple.