After a quick root about in the old Enemy within source book for WHFR in 2512 the Emperors heir was one Wolfgang Holswig-Abenauer, his sisters eldest son. So its safe to say Karl Franz has no kids by that date, and IRC the storm of chaos happened in 2522. So that would make Luitpold 9/10 at the very most.
But the way the fluff keeps changing all the time who knows