Although it seems that Apple has indeed abandoned its line of Wi-Fi routers (even though they are widely praised by it), the latest models continue to receive due support from the company.
Today, almost a year after the last update, Apple has released new firmware versions of the AirPorts Express, Extreme and Time Capsule.
IEEE 802.11ac bases are now receiving version 7.7.9 AirPort Base Station Firmware Update, while the older 802.11n 7.6.9.
As pointed out in the Apple support articles linked above, the updates have to do with that KRACK vulnerability released in mid-October that had already been fixed on all Apple operating systems themselves but not on these routers. They also correct other security holes detected by Ma staff, so they are highly recommended to all users.
Updates can already be applied by AirPort Utility from macOS (located in the / Applications / Utilities / folder) or from his own iOS app: