Erm, iPadOS is just Apple's branding for iOS on the iPad. The iPad Air 2 can currently run the latest operating system iPadOS 14. Do you mean you're concerned about it running iPadOS 15? We'll find out during WWDC next month. If Apple does drop A9-class devices then I think it is likely that the A8X will also be dropped as it shares the same amount of RAM (2GB) and roughly on par performance.