> Personally, I have a hard time guessing which of "extend the life of the human organism to, let's say, 500 years" or "read out the living brain state of a human being and simulate it in a computer" is going to be easier.
The latter is probably closer. We can already induce extended periods of apoxyia in animals by replacing blood with cold saline without brain damage so a similar procedure should be possible to keep healthy brain tissue intact while scanning it. The necessary fidelity of the simulation is what we don't know yet.
Keeping a human being alive for 500 years means knowing how to do roughly the same thing to bodies in order to accomplish the major periodic surgeries necessary to replace failing/injured parts including healing the brain itself, so probably represents a harder technical threshold.