Samsung's representative confirmed to AP the existence of the 300mm f/2.8 XF ED lens prototype spotted in this promotional video three weeks ago. Currently there are no definitive plans to release this lens.
Back in February, Samsung already announced five NX lenses and the 60mm f/2.8 Macro ED OIS SSA seems to be already distributed to testers. A new 700mm NX lens is also expected. This summer Samsung will release two new mirrorless cameras: NX20 and NX200.