I think that this is a natural development and definitely a question of when, rather than if. ES6 would also help with having the output look closer to the input, amongst other things.
It makes sense to bear in mind the target audience of reason, which are likely slightly more agressive with being on the front foot than the norm. Even without that consideration, many businesses have already stopped support of IE11 due to the burden of support vs user base size. By the time an ES6 output could be implemented this will only have moved on even further.
In terms of users that may be on IE, Facebook is probably the outlier here due to the massive userbase (but I think it’s only on messenger.com), so it will likely impact FB much more than the rest of the community.
Given that I would say press on…