Using ARM binaries on x86 hardware
Before you start porting your applications to x86, you may want to check if you have the libhoudini proprietary translation layer available on your device. The Remix OS project (derived from android_x86) uses these libraries to make it possible to run Android on your regular PC. In fact, this makes almost all regular applications in the Play Store work directly from the Play Store application when running on a regular PC.
If all you want to do is revive some old hardware, this is an option worth considering. The only problem is if you need high performance for encryption or similar tasks, since the translation layer slows down execution. Tests with SQLCipher showed that the execution time was three times longer for the same operations, compared to a native environment. This won’t be a problem for projects where you just need to view states of your automated home or how many fish are still alive. If all you need is a simple control interface or to read webmail, you can easily do that even on old hardware.
If you want to play games though, you may be out of luck because many games developers use specialised native code to squeeze every ounce of performance out of your device. This ends up leaving x86 users without support.