I've used tmux inside a single vterm buffer for several years now, and together with vterm-toggle to toggle buffer visibility with a single keypress, it's been a nearly perfect setup (apart from vterm-toggle messing up winner-mode's undo history). I remapped the default tmux operator key to ';' so it kinda logically fits with devil-mode, which I've been using for a few months.

I've also augmented vterm with custom functions, such as I can quickly cd to another dir using ivy completion in the minibuffer, which is much faster than using shell's integrated completion system.