5 man-year to optimize strings?

The always insightful Java Performance Tuning newsletter has one interesting piece on Java strings:
http://www.javaperformancetuning.com/news/news185.shtml


"For JDK 9, Oracle has targeted improving String in this way. Analysis
of String indicates that most Strings are ascii, so Oracle have changed
String to use a byte array instead of a char array. To make this work
efficiently without impacting String performance across all it's uses,
took 5 man years to achieve. In the news items, you can find Aleksey
Shipilev's fascinating talk about exactly why it took so much effort."