Luna should have more time on the screen! She should not be a background pony! At least that's my opinion, we all know Luna is best pony!
Well, I kinda have to agree with the fan theory that Twilight's 'next level of studies' is going to be overseen by Luna, there just seems to be so much pointing to that. So if that's true, that means a lot more Luna screen time
I think Luna and Celestia will play an incredibly vital role, most likely in the finale, but s*** as they say, is about to go down. Besides, Luna had her own episode in Luna Eclipsed, she had her spotlight at least once and that's good enough for me regardless of her background position lately.
As far as I remember (yeah, last time I watched S3-opening is about 2 days ago) Luna looked kinda jealous to me. Maybe Twilight`s task doesn`t fit Lunas thoughts/cut`s her own rights as princess of the night or something. Anyways, I am almost vertain that Luna will make some more appearances than last seasons, and maybe, like said above, play a vital role (in the finale?). Who knows..?^^ Greetings