Wow, thanks for blogging this as I never heard of i3 before and it looks amazingly productive. Makes me want Apple to take the Split View further to the next level on both iOS and OS X, turn it into a tiling WM like i3.
The OS clearly could provide a way to group any number of unrelated windows with tabs, full screen or not, in any tiled arrangement, with more than a lousy 2 splits that are vertical-only. They just don't do it, and they've had decades to add what amounts to some rectangle management.
OSX has third-party tools which go much further than split view. Divvy[0] for instance. They're a far cry from a true tiling WM, but they're way beyond what OSX provides OOTB.
I'll try Divvy again and see if I can stick with it. i3 just feels like the integrated environment with better shortcuts that forces you to stick with it and get used to it sooner. I'll try to install it in VM and see if I'd like it there.
http://www.nrtm.org/index.php/2011/01/28/tiling-window-manag... (2013 so ancient)
I've not used MacOS since around 2011/12 so take this with a pinch of salt.
The real pain is in managing the software that you'd want to run on OSX in X11. The best I've found is NetBSD's pkgsrc, but it's not great on OSX. Even if you are okay building from source, you'll find stuff breaks pretty often. Homebrew isn't really geared toward providing X11 versions of apps, so you can forget that. All in all, much easier to use Ubuntu or FreeBSD and get the benefit of a well-integrated package manager and an X11 environment that isn't a step child.