Technology moves fast and is not likely to slow down. Therefore, cutting-edge knowledge we have today can quickly lose its value. Nevertheless, just as a car that loses a lot, but not all, of its value when you drive off the lot. We also still have value in those old and rusty skills from our past. There are modern needs and baseline knowledge that can be assumed from those past projects. Do not ignore them in an interview or resume.
Migration Is ForeverAn essential part of technology moving forward is that we always have migration projects available. There is a steady stream of new and start-up companies that can dive into new technology from scratch. However, there is also a significant number of organizations that see a need to move old technology to something new. This process often requires knowledge of both the past and the new platform. That is a niche into which you may fall. It has its own challenges, but can be lucrative.
The Value of a Firm FoundationThere are work and experience that come from learning and mastering anything. Even though the platform you learned last year has lost its luster, there are fundamental skills you showed. This situation is most evident with a version upgrade. While there are watershed releases that can nullify prior version knowledge, that is rare. Even big leaps in functionality are almost always built on those past versions. That means you may have old and rusty skills, but those are still useful in the modern version. They might even be close enough for you to be instantly productive.
Staying CurrentYou do not need to work in a specific technology every day to stay current. Once you have "mastered" a technology, it can often be enough to keep up with release changes. One or two versions are often close enough to your core experience when you supplement that knowledge with things like conferences, reading blogs, and watching videos. An added benefit of this approach is that you will likely have a go idea of what you do not know. The more substantial changes in any version will tend to be primary topics for this sort of content. Thus, even though you may not have used the new features, you can still talk intelligently about them.
Episode Challenge: Add a section to your resume or brand site that addresses podcasts, blogs, or tutorials you follow and maybe the type of things you learn from it.