They should add a description for all the timezone abbreviations, cause names like 'yst' and 'yert' don't make much sense and, more important, they should add the periods of time when the zones were effective. 

At the same time, provided the periods are added to the info, I can hardly imagine a php developer who will want to find the right abbreviation for a date (the one that was effective for the date) by scannning the list, because the internal PHP functions like date(), strtotime() and the DateTime class already do it automatically for you whenever they perform date manipulations. 

So I doubt DateTimeZone::listAbbreviations() is needed at all.