The "resurrected couple" thing is needed so that Luthien can have offspring. And Earendil is a mythical figure and as an absent father doomed to be obscure even to his own very wise half-elf son Elrond, not only to us. So we are in very good company here.So true!
Btw. Luthien did leave the circles of the world? But only after her second death finally.Her first one she begs Mandos to release Beren before HE does leave them. I found that resurrected couple thing always odd and never really got it. Just like i was never much into Earendil... i find him obscure at most. But i am waiting for my next SFEE, maybe with next season when we get beren and luthien or season 9 or ten when we get Earendil... (that is... we get Tuor and turin next... is there something else in between, hurin? My guess is 9/10 being the earendil season...)