All of this is possible in the current Emacs. 1. You can already define what program opens a file in dired. You could even use detach it from the Emacs process

All of this is possible in the current Emacs. 1. You can already define what program opens a file in dired. You could even use detach it from the Emacs process so it stays open when Emacs closes. 2 we already have vterm, which has all the features you described. 3. There are ways to make this better. I am actually in the process of writing a blog post about working efficiently over tramp.