Doesn't matter which is more common. All actively developed languages eventually get new keywords and breaking changes. However, most of them will not interfere with existing code running under previously defined behaviors.

Even node 10 applications that use MooTools (i.e. JavaScript executing in a different runtime) will continue to work just fine if `flatten` is added as proposed in node 11+. The developers will eventually need to patch it but it's not like this bug where one day users autoupdate their browser and half the websites they visit are broken.