Those other "features" are just conventions that come with being on a *nix OS. They're aren't unique to i3. But regarding adoption, of course power-tools (for power-users) don't get wide adoption. That's just how things are, since the majority doesn't have the time to put into learning how to use such tools.

This thread is about there being a use for a tab-less browser. That doesn't necessitate wide adoption.

(Not that I'm saying that a tab-less browser is of particular use, since one can just ignore tabs in a tabbed-browser.)