If not supporting IE, a good gauge is evergreen browsers (Chrome, Firefox, Edge) and Safari going back 2 major versions. This means supporting 2 years of Safari 9.x and 10.x as of today. macOS doesn't upgrade as often as evergreen browsers.
http://www.everyi.com/by-capability/maximum-supported-ios-ve...
So it depends a little upon your user demographic (or whether you want to keep supporting users or companies that can’t afford to upgrade their device).
So, while you may be able to get your code to run on them, it might not be a great experience and of limited value to your customers to even try offering support.
During AB tests, sales actually went up