Well, my first reaction to reading this is that vim doesn't need this. What's wrong with opening another terminal Xorg window (like xterm)? If you're not using Xorg because you're in the linux console or through a ssh connection, what's wrong with terminal multiplexers (like tmux)? If Vim was already started when you realized you wanted a shell, what's wrong with Ctrl-Z to get to the parent process shell or :shell to open a shell subprocess?
Vim is a text editor, but now it seems it's a terminal multiplexer, too.
Something I really like about vim is that it stuck closer to the unix philosophy of doing one thing well and being highly compatible with the rest of the OS environment for more features through the universal interface of text. This makes it seem like it's trying to move closer to emacs's way of doing things by having stuff integrated and being a complete development environment instead of letting the whole orchestra of the OS components be the environment.