These ASICs are going to be nearly obsolete by the time anyone plugs them into a socket.
I don't know about that. First gen, yeah probably. But sooner or later ASICs will hit Moore's law or worse like everything else and their usable life will be measured in years (2-5 or more) like other chips.
21's plan, as stated, is pure bullshit. The only question is whether they know it or not.
Probably some of both
But bitcoin technology in the form of an automatic economic actor inside a device could be useful provided there is something for the devices to trade. Could be anything. A wallet and an automatic trader inside every device. They could have something like that in mind.
They said exactly that is part of what they are doing. So where's the big mystery here?
The mystery here is that devices could be paid for by mining. Maybe the general bitcoin society has misunderstood.