I don't know about IE9 being "effectively evergreen" but I can say that the only browser specific bugs we've had to deal with recently have been IE9 so I wouldn

I don't know about IE9 being "effectively evergreen" but I can say that the only browser specific bugs we've had to deal with recently have been IE9 so I wouldn't consider it on the same level as IE10 and IE11. IE9 is the oldest browser we support, and soon we won't support it either.