It's really unfortunate that libcpu didn't take off. Last I checked, they got nowhere with no contributors, and now their site 503s. It was an interesting project.
I think it's more than that. It is not yet clear that this approach can work in the general case without emulation: the halting problem may be in the way.
Correct. If you think about it, the program could prompt the user for the address to jump to, and then the program could go there. In fact, that's exactly what some games (accidentally) do: http://tasvideos.org/2341M.html
It is impossible to solve this statically. This is why dynamic recompilation is more practical.
Thanks for that link; That hack (and the accompanying video) has just become perhaps my favorite thing, ever. Also, it led me to this similarly incredible hack as well:
Sure. It could be argued that "general case" is a bit more restricted than that for actual useful software in the wild, but that would still break any program with a JIT.
It's a very interesting topic. It may be our best chance at preserving software.