The problem with repurposing these devices as perma-plugged-in hubs is they have a battery that could eventually swell from staying plugged in 24/7. You have reports here and there from people whose tablet-on-a-wall (not necessarily iPad) swelled up and bulged against the wall.

Even if the iPad recognizes it's always plugged in and discharges from 100 to 80 occasionally, it's still a use case that increases the chance of battery swelling.

I don't mean this as "Apple knows best, psh, silly customer" but a bit of "that's one reason this exists" and a bit of being annoyed that you can't run tablets battery-less off AC to prevent it.