The current cache key for DateFormat objects is (Locale, skeleton) or (Locale, datestyle, timestyle).
For a given locale, we may have many similar DateFormat objects cached. As DateFormat objects have a large footprint, this caching multiple DateFormat objects per locale may waste memory. As there is talk of adding timezone to the key, this will mean potentially more wasted memory.
I think we can do better without sacrificing much in speed.
This ticket is to explore other options for DateFormat objects and caching such as caching the parts that make up a DateFormat object rather than the DateFormat object.