ScriptDocValues#getDate and ScriptDocValues#getDates are used in 5.x to get ReadableDateTimes from ScriptDocValues of any numeric. In 6.0 we expect folks to get their ReadableDateTimes by calling ScriptDocValues#getValue or ScriptDocValues#getValues on date typed fields. This isn't possible in 5.x currently because date fields return millis-since-epoch from ReadableDateTime#value. In 7.0 we expect everyone will have migrated to getValue/getValues and we can remove getDate/getDates.