Alright, so, I recognize that new molds are expensive and not easy to do extremely often, so I'm going to try and stray away from recommending new armor types (that said, a new Hayabusa would be at the top of that list for me).
This is what I'd personally like to see:
-More recolors of the Copperhead :P
-A remake of the Phantom (it's relatively iconic, and I think would make for a decent larger set if we're doing yearly big sets)
-More of the newer Grunt mold in battlepacks (I think that given their massability, two in a single pack would be a great number to stick to)
-More armor skins! I absolutely love how they came out in Halo Heroes when they came out right (armor printing QC needed some work early on but seems better now)
-Purple! A great color that I don't feel has gotten enough in the new system.
-More Reach colors especially! Mega has been great with giving us a variety of colors for almost every armor mold, but Reach still feels like it's lacking non-realistic or zombie game mode armor color patterns.
-More terrain-oriented sets: I really love the terrain parts Mega produces, and feel like having more of them would be great.
-Any other colors for the new female-style Reach Air Assault armor that was first released as Kat. The helmet mold on that figure is beautiful and I want more of it!