This is so long overdue, but I feel like I've been using Joda Time for so long that the benefit of having it in the platform is kind of outweighed by the hassle of learning a new API.
You'll also find that there will be a release of Jodatime after 310 is finalised that allows it to implement the top level interfaces defined by 310 - eg Temporal. This will allow the libraries to play nicely together and means you'll probably be able to write code like:
LocalDate date = LocalDate.from(someJodaTimeObject);