Elbaf definitely should happen. It'll be where Shanks and his crew lose to Blackbeard. Shanks because his crew got that whole viking theme. It'll also be where Usopp proves he's a great warrior by avenging his father. Could also set up a cool moment where Yasopp dies and that's when Usopp shows his conquerors, if he does have it. It'll also wrap up the last part of the road poneglyph puzzle as Shanks or something elbaf related should be tied to that last road poneglyph.
Laugh Tale will be the final arc of one piece. Then Oda will take a long hiatus (maybe a timeskip happens) and he'll come back and finish the story of how the WG falls. That'll be a 5 year story in and of itself.