If you're using Babel already, WebKit hitting 100% support is irrelevant. IE is going to be the thing that prevents us from running ES6 natively in the browser for several years more.
I was going to reply it wasn't that long, until i realized ie will be around in meaningful numbers for another 4 years. Windows 7 is supported until 2020, and IE is the only game in town there for enterprises. The new distribution policies of w10 will mean plenty of places will run out the clock on w7 support. So, yeah, I guess we're supporting IE 11 for half a decade to come.
I think we're going to see high IE usage in some markets well past that point. Just as an example, almost every Korean website that keep any sensitive data (and many, many that don't), rely on old IE plugins that are never going to be supported by Edge. Although the gov't is now throwing money at developers to rid themselves of the outdated tech, it's going to be a long process.
Chrome JUST took over IE in market share in the last few months here. All other browsers are sub-5%.
IE 11 ships also with Win8.1 and Win10, so IE11 will be around until 2022 or 2025.
IE11 is the new IE6 and will be around a long time in enterprise. Thank you Microsoft. It's epecially annoying as Edge is based just on a refactored and improved trident engine after all, so basically IE12 html engine under hood (and was already called "Edge" in DevTools in IE11).
At the very least, if you use Safari for development you won't need to run Babel every time you change something and want to test it, only for release builds or when you want to test on other browsers, which is nice.
Setting up a build watcher in Grunt/Gulp/etc is really worth the time savings, especially if you use Live Reload. I make a change to a file in vim, and the page reloads with the new build.
There are a lot of node/npm modules that aren't ES6 friendly... unless they pull in and shim out cjs/npm modules, then it will still be some time before it's really useful.
