My 128gb Air 2 Cellular still runs great, has current apple iOS.
Wont need an upgrade at all, very happy with my October 2014 device.
No mate I think Apple make some of the best designed and engineered products on the market. Unfortunately I don't feel the same way about their software. I guess some people like being spoon fed and that's why iOS is still around.
Edit: Oh my one tip is to get one of those trendy covers that double as a stand. My wrists really suffer after 5 or 10 minutes holding the iPad or Tab 4 upright.
@AlistarS I play Bejewelled and thats about it.
Use if for streaming netflix etc on my 1+ hour commute on the train daily.