That being said, while reading the "Why Zed?" page[1] I kept thinking "emacs can already do that" all the way.
"Oh here ... I have made a plane that flies"
"emacs can already do that"
classic.
On the other hand the features described in the page I linked are mostly already built into emacs, at most you need to flip a couple customization switches to get the same idea.
Basically: remove the toolbars, enable ido-mode, use tramp for remote editing. The splitting thing is built in although you'll need to redefine a couple functions to get the exact behaviour shown in the gif (nothing very fancy though).