Blutrabe added a post in a topic Greyjoy storyline
My guess is that they'll cast Euron for S6, and have him do whatever important thing he is going to do in TWOW.
Balon will unceremoniously killed off and Euron will just take his place, without any kingsmoot. Maybe they'll have Asha question his position, but we'll see what happens to her in S5 (if anything).
Euron will not send Victarion anywhere, as he doesn't exist in the show canon and Dany doesn't need him to return to Westeros.
So in short, the whole Ironborn plotline from AFFC/ADWD is cut, but will be picked up with TWOW.