I think that I, like many others who actually do work with their computers had a hard time finding a use for tablets and their invariably locked down, invariably limited software; but I do have one (ok, a couple) that I have learned to make use of. For reading - books - pdf manuals - maps - or just because for that simple reason that it's easier to roll it onto the floor without breaking at 3am after watching some sort of video (nevermind what kind) than a laptop is.
For these, simple reasons - they've already made the ideal device, being basically a screen in some package that will only get out of date because of not being new in 'style', or - as became fashionable - because they glued in the battery. While early gen/particularly cheap tablets are low enough resolution to be noteworthy as a point to upgrade, I certainly don't need a 4k screen on one, and I'm certainly not about to buy a bigger one.
So - what am I going to upgrade? I can only think connectivity (just tether to your phone) or miracast (if it ever worked). Ubuntu's idea of a converged OS/device docking was the only one that might require a powerful device (and yeah; that's still not here); everyone else just wants to sell you a tablet, phone /and/ other device then parasitise your data through their (not calling it cloud) online services.
A better forecast would be when can we have a tablet with the LCARS user interface. At least that came with clearly identifiable, activable UI elements that were large enough to deliberately press.