Q3 Xenos Compendium for RT will have: "Xenos Compendium is a comprehensive collection of countless horrifying denizens of the Koronus Expanse. From the Rak’Gol to the Yu’vath, Orks, Eldar, Daemons, and monsters from countless worlds, Xenos Compendium provides the details necessary to defend yourself"
Yes, it would be stupid if FFG never put out info for Eldar. However, the lines are somewhat compatible for a reason. They divided the settings so they wouldn't have to reprint the same stats over and over again. I just hope the few orks in Mark of the Xenos are suitably different from the ones in RT Core.