If not, what is required for it to start supporting tabs?
If you make your Emacs window fullscreen (green button) then when you press C-x 5 2 the new window will be added as a tab on the existing window.
But as far as I know there's no other way to create tabs, probably because Emacs is missing the standard Window menu where this stuff usually lives.
(I use railwaycat's Mac-specific fork at https://bitbucket.org/mituharu/emacs-mac/overview, so I can't confirm whether this works with the standard distribution. But I'd encourage all Mac users to use that fork anyway.)
I use elscreen for tabs. I don't think you have to rely on the OS to get tabs.
For completeness, this is now available in railwaycat's Mac port with
mac-toggle-tab-bar which seems to have a default binding of