I tend to think the larger size might open up a few more opportunities for it. 4" sucks for anything other than a phone (and even then it's questionable).
I could definitely see using one in our kitchen. I've been looking for a reasonable way to have a decently-sized display with tablet functionality. Making it fixed-mount would actually be a benefit as it'd keep my wife from putting it down on the counter and spilling something on it... again. I've been wanting a decent one for my desk also.
That and I wouldn't mind having one that size for my desk. I end up having a tablet there, and it pretty much stays right there next to a cordless phone. Combining them would cut down on the number of devices.
Trouble with the bluetooth handset is you introduce another layer of hassles (charging it, keeping it handy, etc). At least with an all-in-one it'd have a chance of 'staying together'. That and one would imagine the wired version would have it's own POTS line connection, useful for situations not wanting wifi or being set up for ethernet VOIP.
I'd imagine the projected $500 price-point is a bit steep for most typical residences. Still, for all-in-one there's something to be said for paying the price to get the built-in integration.
As for industry migration, I think it's clear the industry has seen it's share of failures. I'd lay the blame more on lack of interoperability and closed-systems than the form factor or the price point. Nobody's wanted a locked-in system. Granted, a lot of the devices littering the graveyard of dead tech probably got there more due to the limits of hardware at the time than anything else. That they were locked-in and expensive wasn't helped by the fact they were also dog-slow.
