In the Redmond dialect of Microspeak, we talk about extensibility: Designing a system with specific points where features can be added in the future, often by outside parties. For example, an example of an extensibility point in the shell would be a context menu handler or a namespace extension.
In the Reading dialect of Microspeak, the term for this is future-proofing.
On the other hand, if you use the term future-proofing in Redmond, people will interpret it differently. In Redmond, future-proofing means designing a system so that it continues to function without alteration, even if something happens in the future. (For example, one example of future-proofing—in the Redmond sense of the term—would be using a function like
SHGetSpecialFolderPath instead of hard-coding the path to a directory.)
Update: Some folks have taken issue with this definition, and I will have to defer to their local knowledge. I get my reports on the Reading dialect of Microspeak from my contacts there, so it's possible that they were mistaken, or that the usage was peculiar to their workgroup and incorrectly extrapolated to the entire dialect.