Sorry, our crystal ball is broken, so it will no longer predict the future accurately.
Regardless of when a product might be officially discontinued by Apple, the "issues" on the AirPorts generally tend to start picking up at about 7-8 years of use on the AirPort Extreme and AirPort Express and 5-6 years on the AirPort Time Capsule since it has more "moving parts".
The last security update issued by Apple was about 3 years ago. WPA2 Wi-Fi Security is still adequate for most home users, but the users who insist on the latest and greatest started switching to other routers a few years ago.
I'm probably going to continue using the 2 AirPort Extremes here for another 18-24 months, at which time they will be about 8 years old. The AirPorts have been flawless for many years here. The only problem........relatives still want to visit just to use the wireless.