[xutopia]

Which both worlds?

[aban]

The extensibility of Emacs, along with Vi[m] key bindings.

Although Spacemacs does have a "Holy mode" which will keep the Emacs bindings and won't use vim-like keys.

[CrystalCuckoo]

Probably modal editing and plugins that aren't constrained by Vimscript.

[quarterto]

Presumably Emacs and Vim.