Makes sense, and perhaps I should revert that method to it's original implementation, and handle this in a different Issue. 

The reasoning for changing the output is described in the description of this pull request. The background is we regularly get tickets from our users who say they get confused when they can't find the time zone (or country or language or etc.) in the (long) list below the separator where they would expect to find the value. This usually happens when a user goes into edit mode and a non-priority option is selected, and they want to change it to a different selection. It's not obvious they then have to look at the top (as the top is often also out of sight). The implementation of `options_for_select` always renders all options below the separator, regardless if an option is a "priority" option or not. To be consistent I thought it would be better if time_zone_select behaves the same. 

Note that this change in output should not have any ill effect on existing applications, you'd only get to see more options.