Ivan Seeking said:
I too have heard a good number of people working at high levels in AI making the claim that "uploading" the mind will one day be possible. For starters, I don't see how that claim can be made since we can't yet quantify consciousness or self-identity. So, at a minimum, at this time there is no way to say if a person's consciousnes could ever be transferred in such a manner. We could never know if it really is good ole Joe, or just a fascimile.
You seem to be arguing for duality, which there is no evidence for (physical "brain states" correspond 1-1 with "mind states", to within accuracy of measurement).
Even if it isn't eventually possible to "upload" onto a traditional computer architecture, there have been several recent attempts to simulate brain function directly, using massively parallel systems, and/or using artificial neurons (that is, computer chips designed to behave like neurons). There is no reason to think that such a system, were it able to reproduce the connectivity of the human brain, could not have a person's consciousness copied onto it.
The other alternative is to grow a new brain out of biological tissue (stem cell research could help us with this), and then somehow imprint the brain state of a person onto this "blank". Even if there were some fundamental reason that brain states cannot be replicated by silicon chips, there is no plausible explanation as to why replicating the biological brain directly wouldn't work.
To respond directly to the OP:
The only plausible reason why "eternal consciousness" (to within thermodynamic limits on the universe, and/or our capability of harnessing energy) would be impossible would be if the emergent property we call consciousness were somehow self-limiting. That is, if the conditions necessary for consciousness to exist and continue, necessitate the eventual termination of that consciousness. I don't see this as very likely, so I believe one day we will achieve this, assuming we don't go extinct first.