Linux is an example of software with a Rapid Development Lifecycle. It's created, used, feedback is received, modified, used, feedback is received, etc.
Usually the process of modification is largely realised through addition of features and code, which has been the case with a lot of Linux development. Right now the Linux kernel code base is undergoing something of a revision, where the addition of code and features is less important than the improvement of existing features.
If Linux were developed under a different model, such as the Waterfall development model, then this could easily be seen as a sign that its development were drawing to a close with the finalisation of features. But since Linux uses Rapid Development, all the current revisions signify is that the developers are making sure they have a solid foundation for later improvements.
I don't see the Linux lifecycle ending any time soon. It may fragment in the next few years, in my view, but it's not about to die.