Will anyone actually going to upgrade from iPad Air to iPad Air 2 just for TouchID? The current iPad Air and iPad mini are fast enough for next two or three year. I personally won't upgrade just because of TouchID..Apple need to bring something really different to the tablet to lure iPad Air user to upgrade
I don't think iPads are meant to be upgraded every generation. It's ok to skip one or two.
That said, the lack of Touch ID was the main reason why I did not upgrade my iPad 4. When the next iPad Air will have Touch ID and, I very much hope, more RAM, I'll definitely upgrade.