I found this concept art by a Halo concept artist.. I posted it on Bungie some time ago. The artist promtly removed it from his web page. I think it maybe a GRD Helmet concept. I also feel that GRD is somekind of early version of Hyabusa. I prefer to call it Bobusa. These ideas are pure speculation. Time will tell.
Unlikely. This was a hot topic in the ODST release.
It simply cant be added, it would need to have been data implemented in the original game otherwise players without the anniversary disc couldnt play with those who did. The easiest example is the Recon Armor of H3, It was always installed in every H3 it was just locked like every other armor type only Bungie had to unlock it personally for you to use it. Adding a new armor all together was impossible then and I believe Bungie used the same programming in reach so it is likely impossible now aswell.
As for the pic of it in game, it is very possibly modded in.
The Hyabusa was contract trade done between Bungie and Team Ninja so DOA could use a Spartan in their game, in exchange Bungie would get rights to add a armor variant based on Ryu Hyabusa armor from Ninja Gaiden, there was no Prototype of the Hyabusa that strayed that far from Ryu’s armor