In the first episode of nightfall we saw the Halo 4 model Elite but in the prologue/epilogue of H2A we saw the amazing H4/Classic blend from Halo 2 Anniversary.
It’s different factions. Jul’s Covenant and Arbiter’s Covenant are of different race/ethnicity and wear different armor. Halo: Escalation shows both Halo 3 Elites and Halo 4 Elites.
Keep in mind that the new Prologue and Epilogue were reusing assets from the H2A cutscenes, and shouldn’t be used as an indication of anything outside of Locke and Thel’s appearances. Overall they’ll stick to the Halo 4 style. Even Thel’s model from the prologue and epilogue draws a lot from that style. Their armour may be more traditional and I would expect to see different skin tones.
Probably like the ones in halo 4