One of the problems tmux and friends don't solve that a "smarter" underlying system might add is the ability to make the choice to detach a process or redirect

One of the problems tmux and friends don't solve that a "smarter" underlying system might add is the ability to make the choice to detach a process or redirect its output after it's already begun running. For example, I specifically have had on many occasions started something and then later wished I'd previously started screen. While, "gain the knowledge to better configure your environment to start" is a valid response, equally valid is a desire for a more flexible default environment in general.