The armour/gear of the Kingsglaive isnt necessarily ONLY linked to the movie though. FFXV has it as gear for Gladio, Ignis and Prompto. I mean yeah its mainly from the movie but overall if we only got Luna or Noctis gear i feel like it would be a bit of a letdown. Lunas dress is awesome and all but noctis gear is a bit...meh and can already be replicated ingame with glamour items.

If they were to do a crossover event (I made a thread about this a while back) then from the only real point in the game that we could meet Noctis, receiving Kingsglaive gear feels more appropriate. He comes to Eorzea in preparation and we either help or protect him as he does. It would be more rewarding if we got the gear which signifies the role we played for noctis during his time in Eorzea rather than just his and lunas attire.