hi
I think paper is going away.
How long will it take? ... I don't know.
10-15 years I suppose.
Look at what happened in photography, now you cannot buy a fil camera any longer, it's gone digital.
Of course we'll need better resolution, colors, flexible display and what not... but it's coming.
As for Adobe I think they're well aware what this means to PDF.
They're smart folks, they'll figure it out.

I think it can be more than adding reflow capability... depends on how "live" books will become with shared annotations, updates etc.