Apple has bad habit to install absolutely minimum amounts of RAM into their mobile devices. iPhone had 2 GB RAM when Androids (with similar price) had 8 GB RAM. It means that RAM will be main issue for supporting those devices in the future iOS versions and eventually they'll be dropped, despite extremely powerful CPU and huge storage.

But with 16 GB it won't be the case ever. And, of course, CPU will not significantly progress in the future and certainly will not the limiting factor. So this tablet should easily last for another 10 years (if battery could be replaced with reasonable efforts).