When I saw the raw I have the feeling that the episode is going to compensate the owned that Ranka gets on 19 but in the end Ranka realizes that her songs never reaches Alto, so she decides to leave (run away) because she believes she's already lost the love triangle. I can assume that all of us here are expecting that she returns to save the Frontier's dommsday with a huge vajra army to kick Grace & Co. asses. Untill now, while I still preffer an AltoxSheryl end, I have the feeling that the triangle will ends unclaeared
Now the Grace & Co.is the next point, Brera helps Ranka on his own will or he act under Grace orders? Probably is the first because he really cares about her but we are aware of the Grace's "forced mode" This fit very well on her plans, They leave and she engages the force mode so Brera kidnaps Ranka and take her to Macross Galaxy, but if it is the opposite still works for their plans. So Grace lefts Leon with a seemingly nonworking Queen Sheryl meanwhile they have the little queen seized in Galaxy ready to start the final battle.
To finish (If I continue speculating thinking as everything it fits in only 4 eps xD), I can't blame the Alto-Hime for his attitude against Ai-kun, but I ask myself what face will put Luca when he learns that he was helping a Traitor xD