I bought my Air 2 with the intent to keep it for the next few years. The A8X is more powerful than any app can take advantage of, the RAM is plenty for me, the display is already higher than 1080p and the battery life is superb. All in an incredibly thin, light form factor.
Unless Apple releases something completely new, I won't be upgrading to the Air 3 (or Air 4 for that matter).