I think it's FAR too early to start predicting the 2017 iPad's demise.
The problem with trying to predict these updates is that we really don't know what Apple has up their sleeve. iOS 12 and 13 could be stability updates with a few features sprinkled in here or there. OR iOS 13 might be the version where they really revolutionize iOS and build a very different OS that supports more types of devices.
The other problem is, of course, defining what the demise of a device is. The iPad Mini 2 still supports iOS 11, but there are those who would say the last "useable" OS was iOS 9.
If we're talking purely "Apple Cutoff", then I would say the 2017 iPad still has quite a few updates ahead of it.